feat: multi-subscription support (1 user = N subscriptions)
- Add MULTI_TARIFF_ENABLED feature flag for gradual rollout
- Migration 0041: remove unique constraint on subscriptions.user_id
- Migration 0042: add remnawave_short_id (NOT NULL, UNIQUE) to subscriptions
- Each subscription gets its own Remnawave user (user_{tg_id}_{short_id})
- Add _resolve_subscription() to all 30+ bot handlers for per-subscription routing
- Add my_subscriptions.py with list/detail views and delegation handlers
- Refactor cabinet subscription.py (4687 lines -> 10 focused modules)
- Add subscription_id parameter to all cabinet API endpoints
- Adapt all services: autopay, wheel, contests, campaign, guest purchase,
monitoring, blocked users, account merge, promo codes, payments
- Replace all user.subscription (singular) with user.subscriptions iteration
- IDOR protection via get_subscription_by_id_for_user on all endpoints
- Full backward compatibility: MULTI_TARIFF_ENABLED=False = legacy behavior
c0mrade
335be66980