- Add sqlx migration system with migrations/ directory
- Create 001_init.sql and 002_push_subscriptions.sql migration files
- Move from manual CREATE TABLE to version-controlled migrations
- Add push_subscriptions table with DB persistence
- PushSubscriptionStore now loads from DB on startup
- Add save/remove/get methods for push subscriptions in db.rs
- Move VAPID keys to .env file (with fallback to hardcoded values)
- Delete old vibetorrent.db and recreate with migrations
