feat: add user submission history page

Allow users to view their own past submissions (code, size, status,
timestamp) for each game. Adds API endpoint, backend handler, SQL query,
and frontend page with expandable code display.

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

1 files changed, 38 insertions, 0 deletions

diff --git a/backend/api/handler.go b/backend/api/handler.go
index 8d0d9be..57ae973 100644
--- a/backend/api/handler.go
+++ b/backend/api/handler.go
@@ -376,6 +376,44 @@ func (h *Handler) GetGameWatchRanking(ctx context.Context, request GetGameWatchR
 	}, nil
 }
 
+func (h *Handler) GetGamePlaySubmissions(ctx context.Context, request GetGamePlaySubmissionsRequestObject, user *db.User) (GetGamePlaySubmissionsResponseObject, error) {
+	gameID := request.GameID
+
+	_, err := h.q.GetGameByID(ctx, int32(gameID))
+	if err != nil {
+		if errors.Is(err, pgx.ErrNoRows) {
+			return GetGamePlaySubmissions404JSONResponse{
+				Message: "Game not found",
+			}, nil
+		}
+		return nil, echo.NewHTTPError(http.StatusInternalServerError, err.Error())
+	}
+
+	rows, err := h.q.GetSubmissionsByGameIDAndUserID(ctx, db.GetSubmissionsByGameIDAndUserIDParams{
+		GameID: int32(gameID),
+		UserID: user.UserID,
+	})
+	if err != nil {
+		return nil, echo.NewHTTPError(http.StatusInternalServerError, err.Error())
+	}
+
+	submissions := make([]Submission, len(rows))
+	for i, row := range rows {
+		submissions[i] = Submission{
+			SubmissionID: int(row.SubmissionID),
+			GameID:       int(row.GameID),
+			Code:         row.Code,
+			CodeSize:     int(row.CodeSize),
+			Status:       ExecutionStatus(row.Status),
+			CreatedAt:    row.CreatedAt.Time.Unix(),
+		}
+	}
+
+	return GetGamePlaySubmissions200JSONResponse{
+		Submissions: submissions,
+	}, nil
+}
+
 func (h *Handler) PostGamePlayCode(ctx context.Context, request PostGamePlayCodeRequestObject, user *db.User) (PostGamePlayCodeResponseObject, error) {
 	gameID := request.GameID