refactor(quota): migrate traffic quota from tunnel to user level

- Replace tunnel_quota table with user_quota table
- Add user-level daily/monthly quota tracking and enforcement
- Update user CRUD to include quota configuration
- Migrate backup/restore to use user quota fields
- Update frontend API and UI for user quota management

go-backend/internal/http/handler/jobs.go

@@ -136,7 +136,7 @@ func (h *Handler) runResetAndExpiryJob(now time.Time) {
 	}
 
 	h.resetMonthlyFlow(now)
-	h.resetTunnelQuotaWindows(now)
+	h.resetUserQuotaWindows(now)
 	h.disableExpiredUsers(now.UnixMilli())
 	h.disableExpiredUserTunnels(now.UnixMilli())
 }