feat: refactor tournament to generic DB-backed N-person bracket

Replace hardcoded 6-person tournament with a generic single-elimination
bracket system backed by new DB tables (tournaments, tournament_entries,
tournament_matches). Includes admin CRUD, standard seeding algorithm,
bye handling, and a CSS Grid bracket renderer on the frontend.

Add comprehensive tests for backend API/admin handlers, seeding logic,
and frontend bracket component.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

3 files changed, 280 insertions, 0 deletions

diff --git a/backend/db/models.go b/backend/db/models.go
index c4a713d..3086c3b 100644
--- a/backend/db/models.go
+++ b/backend/db/models.go
@@ -74,6 +74,29 @@ type TestcaseResult struct {
 	CreatedAt        pgtype.Timestamp
 }
 
+type Tournament struct {
+	TournamentID int32
+	DisplayName  string
+	BracketSize  int32
+	NumRounds    int32
+	CreatedAt    pgtype.Timestamp
+}
+
+type TournamentEntry struct {
+	TournamentEntryID int32
+	TournamentID      int32
+	UserID            int32
+	Seed              int32
+}
+
+type TournamentMatch struct {
+	TournamentMatchID int32
+	TournamentID      int32
+	Round             int32
+	Position          int32
+	GameID            *int32
+}
+
 type User struct {
 	UserID      int32
 	Username    string
diff --git a/backend/db/querier.go b/backend/db/querier.go
index 89d4b55..3b9545a 100644
--- a/backend/db/querier.go
+++ b/backend/db/querier.go
@@ -17,11 +17,16 @@ type Querier interface {
 	CreateSubmission(ctx context.Context, arg CreateSubmissionParams) (int32, error)
 	CreateTestcase(ctx context.Context, arg CreateTestcaseParams) (int32, error)
 	CreateTestcaseResult(ctx context.Context, arg CreateTestcaseResultParams) error
+	CreateTournament(ctx context.Context, arg CreateTournamentParams) (int32, error)
+	CreateTournamentEntry(ctx context.Context, arg CreateTournamentEntryParams) error
+	CreateTournamentMatch(ctx context.Context, arg CreateTournamentMatchParams) error
 	CreateUser(ctx context.Context, username string) (int32, error)
 	CreateUserAuth(ctx context.Context, arg CreateUserAuthParams) error
 	DeleteExpiredSessions(ctx context.Context) error
 	DeleteSession(ctx context.Context, sessionID string) error
 	DeleteTestcase(ctx context.Context, testcaseID int32) error
+	DeleteTournamentEntries(ctx context.Context, tournamentID int32) error
+	DeleteTournamentMatches(ctx context.Context, tournamentID int32) error
 	GetGameByID(ctx context.Context, gameID int32) (GetGameByIDRow, error)
 	GetLatestState(ctx context.Context, arg GetLatestStateParams) (GetLatestStateRow, error)
 	GetLatestStatesOfMainPlayers(ctx context.Context, gameID int32) ([]GetLatestStatesOfMainPlayersRow, error)
@@ -32,6 +37,7 @@ type Querier interface {
 	GetSubmissionsByGameID(ctx context.Context, gameID int32) ([]Submission, error)
 	GetTestcaseByID(ctx context.Context, testcaseID int32) (Testcase, error)
 	GetTestcaseResultsBySubmissionID(ctx context.Context, submissionID int32) ([]TestcaseResult, error)
+	GetTournamentByID(ctx context.Context, tournamentID int32) (Tournament, error)
 	GetUserAuthByUsername(ctx context.Context, username string) (GetUserAuthByUsernameRow, error)
 	GetUserByID(ctx context.Context, userID int32) (User, error)
 	GetUserBySession(ctx context.Context, sessionID string) (User, error)
@@ -45,6 +51,9 @@ type Querier interface {
 	ListTestcases(ctx context.Context) ([]Testcase, error)
 	ListTestcasesByGameID(ctx context.Context, gameID int32) ([]Testcase, error)
 	ListTestcasesByProblemID(ctx context.Context, problemID int32) ([]Testcase, error)
+	ListTournamentEntries(ctx context.Context, tournamentID int32) ([]ListTournamentEntriesRow, error)
+	ListTournamentMatches(ctx context.Context, tournamentID int32) ([]TournamentMatch, error)
+	ListTournaments(ctx context.Context) ([]Tournament, error)
 	ListUsers(ctx context.Context) ([]User, error)
 	RemoveAllMainPlayers(ctx context.Context, gameID int32) error
 	SyncGameStateBestScoreSubmission(ctx context.Context, arg SyncGameStateBestScoreSubmissionParams) error
@@ -56,6 +65,8 @@ type Querier interface {
 	UpdateProblem(ctx context.Context, arg UpdateProblemParams) error
 	UpdateSubmissionStatus(ctx context.Context, arg UpdateSubmissionStatusParams) error
 	UpdateTestcase(ctx context.Context, arg UpdateTestcaseParams) error
+	UpdateTournament(ctx context.Context, arg UpdateTournamentParams) error
+	UpdateTournamentMatchGame(ctx context.Context, arg UpdateTournamentMatchGameParams) error
 	UpdateUser(ctx context.Context, arg UpdateUserParams) error
 	UpdateUserIconPath(ctx context.Context, arg UpdateUserIconPathParams) error
 }
diff --git a/backend/db/query.sql.go b/backend/db/query.sql.go
index 1d6d11c..50aa02e 100644
--- a/backend/db/query.sql.go
+++ b/backend/db/query.sql.go
@@ -186,6 +186,57 @@ func (q *Queries) CreateTestcaseResult(ctx context.Context, arg CreateTestcaseRe
 	return err
 }
 
+const createTournament = `-- name: CreateTournament :one
+INSERT INTO tournaments (display_name, bracket_size, num_rounds)
+VALUES ($1, $2, $3)
+RETURNING tournament_id
+`
+
+type CreateTournamentParams struct {
+	DisplayName string
+	BracketSize int32
+	NumRounds   int32
+}
+
+func (q *Queries) CreateTournament(ctx context.Context, arg CreateTournamentParams) (int32, error) {
+	row := q.db.QueryRow(ctx, createTournament, arg.DisplayName, arg.BracketSize, arg.NumRounds)
+	var tournament_id int32
+	err := row.Scan(&tournament_id)
+	return tournament_id, err
+}
+
+const createTournamentEntry = `-- name: CreateTournamentEntry :exec
+INSERT INTO tournament_entries (tournament_id, user_id, seed)
+VALUES ($1, $2, $3)
+`
+
+type CreateTournamentEntryParams struct {
+	TournamentID int32
+	UserID       int32
+	Seed         int32
+}
+
+func (q *Queries) CreateTournamentEntry(ctx context.Context, arg CreateTournamentEntryParams) error {
+	_, err := q.db.Exec(ctx, createTournamentEntry, arg.TournamentID, arg.UserID, arg.Seed)
+	return err
+}
+
+const createTournamentMatch = `-- name: CreateTournamentMatch :exec
+INSERT INTO tournament_matches (tournament_id, round, position)
+VALUES ($1, $2, $3)
+`
+
+type CreateTournamentMatchParams struct {
+	TournamentID int32
+	Round        int32
+	Position     int32
+}
+
+func (q *Queries) CreateTournamentMatch(ctx context.Context, arg CreateTournamentMatchParams) error {
+	_, err := q.db.Exec(ctx, createTournamentMatch, arg.TournamentID, arg.Round, arg.Position)
+	return err
+}
+
 const createUser = `-- name: CreateUser :one
 INSERT INTO users (username, display_name, is_admin)
 VALUES ($1, $1, false)
@@ -242,6 +293,26 @@ func (q *Queries) DeleteTestcase(ctx context.Context, testcaseID int32) error {
 	return err
 }
 
+const deleteTournamentEntries = `-- name: DeleteTournamentEntries :exec
+DELETE FROM tournament_entries
+WHERE tournament_id = $1
+`
+
+func (q *Queries) DeleteTournamentEntries(ctx context.Context, tournamentID int32) error {
+	_, err := q.db.Exec(ctx, deleteTournamentEntries, tournamentID)
+	return err
+}
+
+const deleteTournamentMatches = `-- name: DeleteTournamentMatches :exec
+DELETE FROM tournament_matches
+WHERE tournament_id = $1
+`
+
+func (q *Queries) DeleteTournamentMatches(ctx context.Context, tournamentID int32) error {
+	_, err := q.db.Exec(ctx, deleteTournamentMatches, tournamentID)
+	return err
+}
+
 const getGameByID = `-- name: GetGameByID :one
 SELECT game_id, game_type, is_public, display_name, duration_seconds, created_at, started_at, games.problem_id, problems.problem_id, title, description, language, sample_code FROM games
 JOIN problems ON games.problem_id = problems.problem_id
@@ -643,6 +714,25 @@ func (q *Queries) GetTestcaseResultsBySubmissionID(ctx context.Context, submissi
 	return items, nil
 }
 
+const getTournamentByID = `-- name: GetTournamentByID :one
+SELECT tournament_id, display_name, bracket_size, num_rounds, created_at FROM tournaments
+WHERE tournament_id = $1
+LIMIT 1
+`
+
+func (q *Queries) GetTournamentByID(ctx context.Context, tournamentID int32) (Tournament, error) {
+	row := q.db.QueryRow(ctx, getTournamentByID, tournamentID)
+	var i Tournament
+	err := row.Scan(
+		&i.TournamentID,
+		&i.DisplayName,
+		&i.BracketSize,
+		&i.NumRounds,
+		&i.CreatedAt,
+	)
+	return i, err
+}
+
 const getUserAuthByUsername = `-- name: GetUserAuthByUsername :one
 SELECT users.user_id, username, display_name, icon_path, is_admin, label, created_at, user_auth_id, user_auths.user_id, auth_type, password_hash FROM users
 JOIN user_auths ON users.user_id = user_auths.user_id
@@ -1054,6 +1144,123 @@ func (q *Queries) ListTestcasesByProblemID(ctx context.Context, problemID int32)
 	return items, nil
 }
 
+const listTournamentEntries = `-- name: ListTournamentEntries :many
+SELECT tournament_entries.tournament_entry_id, tournament_entries.tournament_id, tournament_entries.user_id, tournament_entries.seed, users.user_id, users.username, users.display_name, users.icon_path, users.is_admin, users.label, users.created_at
+FROM tournament_entries
+JOIN users ON tournament_entries.user_id = users.user_id
+WHERE tournament_entries.tournament_id = $1
+ORDER BY tournament_entries.seed
+`
+
+type ListTournamentEntriesRow struct {
+	TournamentEntryID int32
+	TournamentID      int32
+	UserID            int32
+	Seed              int32
+	UserID_2          int32
+	Username          string
+	DisplayName       string
+	IconPath          *string
+	IsAdmin           bool
+	Label             *string
+	CreatedAt         pgtype.Timestamp
+}
+
+func (q *Queries) ListTournamentEntries(ctx context.Context, tournamentID int32) ([]ListTournamentEntriesRow, error) {
+	rows, err := q.db.Query(ctx, listTournamentEntries, tournamentID)
+	if err != nil {
+		return nil, err
+	}
+	defer rows.Close()
+	var items []ListTournamentEntriesRow
+	for rows.Next() {
+		var i ListTournamentEntriesRow
+		if err := rows.Scan(
+			&i.TournamentEntryID,
+			&i.TournamentID,
+			&i.UserID,
+			&i.Seed,
+			&i.UserID_2,
+			&i.Username,
+			&i.DisplayName,
+			&i.IconPath,
+			&i.IsAdmin,
+			&i.Label,
+			&i.CreatedAt,
+		); err != nil {
+			return nil, err
+		}
+		items = append(items, i)
+	}
+	if err := rows.Err(); err != nil {
+		return nil, err
+	}
+	return items, nil
+}
+
+const listTournamentMatches = `-- name: ListTournamentMatches :many
+SELECT tournament_match_id, tournament_id, round, position, game_id FROM tournament_matches
+WHERE tournament_id = $1
+ORDER BY round, position
+`
+
+func (q *Queries) ListTournamentMatches(ctx context.Context, tournamentID int32) ([]TournamentMatch, error) {
+	rows, err := q.db.Query(ctx, listTournamentMatches, tournamentID)
+	if err != nil {
+		return nil, err
+	}
+	defer rows.Close()
+	var items []TournamentMatch
+	for rows.Next() {
+		var i TournamentMatch
+		if err := rows.Scan(
+			&i.TournamentMatchID,
+			&i.TournamentID,
+			&i.Round,
+			&i.Position,
+			&i.GameID,
+		); err != nil {
+			return nil, err
+		}
+		items = append(items, i)
+	}
+	if err := rows.Err(); err != nil {
+		return nil, err
+	}
+	return items, nil
+}
+
+const listTournaments = `-- name: ListTournaments :many
+SELECT tournament_id, display_name, bracket_size, num_rounds, created_at FROM tournaments
+ORDER BY tournament_id
+`
+
+func (q *Queries) ListTournaments(ctx context.Context) ([]Tournament, error) {
+	rows, err := q.db.Query(ctx, listTournaments)
+	if err != nil {
+		return nil, err
+	}
+	defer rows.Close()
+	var items []Tournament
+	for rows.Next() {
+		var i Tournament
+		if err := rows.Scan(
+			&i.TournamentID,
+			&i.DisplayName,
+			&i.BracketSize,
+			&i.NumRounds,
+			&i.CreatedAt,
+		); err != nil {
+			return nil, err
+		}
+		items = append(items, i)
+	}
+	if err := rows.Err(); err != nil {
+		return nil, err
+	}
+	return items, nil
+}
+
 const listUsers = `-- name: ListUsers :many
 SELECT user_id, username, display_name, icon_path, is_admin, label, created_at FROM users
 ORDER BY users.user_id
@@ -1305,6 +1512,45 @@ func (q *Queries) UpdateTestcase(ctx context.Context, arg UpdateTestcaseParams)
 	return err
 }
 
+const updateTournament = `-- name: UpdateTournament :exec
+UPDATE tournaments
+SET display_name = $2, bracket_size = $3, num_rounds = $4
+WHERE tournament_id = $1
+`
+
+type UpdateTournamentParams struct {
+	TournamentID int32
+	DisplayName  string
+	BracketSize  int32
+	NumRounds    int32
+}
+
+func (q *Queries) UpdateTournament(ctx context.Context, arg UpdateTournamentParams) error {
+	_, err := q.db.Exec(ctx, updateTournament,
+		arg.TournamentID,
+		arg.DisplayName,
+		arg.BracketSize,
+		arg.NumRounds,
+	)
+	return err
+}
+
+const updateTournamentMatchGame = `-- name: UpdateTournamentMatchGame :exec
+UPDATE tournament_matches
+SET game_id = $2
+WHERE tournament_match_id = $1
+`
+
+type UpdateTournamentMatchGameParams struct {
+	TournamentMatchID int32
+	GameID            *int32
+}
+
+func (q *Queries) UpdateTournamentMatchGame(ctx context.Context, arg UpdateTournamentMatchGameParams) error {
+	_, err := q.db.Exec(ctx, updateTournamentMatchGame, arg.TournamentMatchID, arg.GameID)
+	return err
+}
+
 const updateUser = `-- name: UpdateUser :exec
 UPDATE users
 SET