refactor(api): separate business logic into game, tournament, session packages

Extract business logic from api/handler.go into dedicated service packages:
- session: context helpers (resolves admin → api import dependency)
- game: game state, code submission, ranking, watch logic
- tournament: bracket construction and seed ordering
- api/convert.go: domain → API type conversion functions

api/handler.go is now a thin adapter that delegates to services and
maps domain errors to HTTP status codes.

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

1 files changed, 2 insertions, 2 deletions

diff --git a/backend/admin/handler.go b/backend/admin/handler.go
index 8eac425..09303ac 100644
--- a/backend/admin/handler.go
+++ b/backend/admin/handler.go
@@ -14,9 +14,9 @@ import (
 	"github.com/labstack/echo/v4"
 
 	"albatross-2026-backend/account"
-	"albatross-2026-backend/api"
 	"albatross-2026-backend/config"
 	"albatross-2026-backend/db"
+	"albatross-2026-backend/session"
 )
 
 var jst = time.FixedZone("Asia/Tokyo", 9*60*60)
@@ -39,7 +39,7 @@ func NewHandler(q db.Querier, txm db.TxManager, hub GameHub, conf *config.Config
 func (h *Handler) newAdminMiddleware() echo.MiddlewareFunc {
 	return func(next echo.HandlerFunc) echo.HandlerFunc {
 		return func(c echo.Context) error {
-			user, ok := api.GetUserFromContext(c.Request().Context())
+			user, ok := session.GetUserFromContext(c.Request().Context())
 			if !ok {
 				return c.Redirect(http.StatusSeeOther, h.conf.BasePath+"login")
 			}