feat: add app user routes (logout, user-info, avatar, tickets)

- Logout: clear device sessions on logout
- User info: return expiry/balance based on billing type
- Avatar upload: support jpg/png/gif/webp, max 2MB
- App tickets: create, reply, close tickets for app users
- Add ClosedAt field to Ticket model

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

backend/internal/router/app/app.go

@@ -8,6 +8,8 @@ func SetupRoutes(r *gin.RouterGroup) {
 	SetupPaymentRoutes(r)
 	SetupAccountRoutes(r)
 	SetupDynamicRoutes(r)
+	SetupUserRoutes(r)
+	SetupTicketRoutes(r)
 }
 
 func SetupAuthRoutes(r *gin.RouterGroup) {