fix: stabilize auth-to-tenant flow and correct tenant header mapping

Resolve post-login routing and tenant context issues by proxying frontend API
calls, redirecting authenticated users away from /login, and hardening club
loading with retries/loading guards.

Align tenant identity end-to-end by returning tenantId in /api/clubs/me and
sending X-Tenant-Id from cookie-backed tenantId instead of local clubId,
restoring authorized tasks/shifts data access after club selection.

backend/WorkClub.Api/Services/ClubService.cs

@@ -112,7 +112,8 @@ public class ClubService
                         clubId.Value,
                         clubName,
                         sportTypeEnum,
-                        memberCount
+                        memberCount,
+                        Guid.Parse(tenantId)
                     ));
                 }
             }