Add OpenAPI docs, frontend, migrations, and API updates

- OpenAPI: add missing endpoints (add-from-url, subscriptions, public availability)
- OpenAPI: CalendarSubscription schema, Subscriptions tag
- Frontend app
- Migrations: count_for_availability, subscriptions_sync, user_preferences, calendar_settings
- Config, rate limit, auth, calendar, booking, ICS, availability, user service updates

Made-with: Cursor

migrations/000005_user_preferences.up.sql

@@ -0,0 +1,10 @@
+-- Add user preferences columns
+ALTER TABLE users ADD COLUMN week_start_day SMALLINT NOT NULL DEFAULT 0;
+ALTER TABLE users ADD COLUMN date_format TEXT NOT NULL DEFAULT 'MM/dd/yyyy';
+ALTER TABLE users ADD COLUMN time_format TEXT NOT NULL DEFAULT '12h';
+ALTER TABLE users ADD COLUMN default_event_duration_minutes INTEGER NOT NULL DEFAULT 60;
+ALTER TABLE users ADD COLUMN default_reminder_minutes INTEGER NOT NULL DEFAULT 10;
+ALTER TABLE users ADD COLUMN show_weekends BOOLEAN NOT NULL DEFAULT true;
+ALTER TABLE users ADD COLUMN working_hours_start TEXT NOT NULL DEFAULT '09:00';
+ALTER TABLE users ADD COLUMN working_hours_end TEXT NOT NULL DEFAULT '17:00';
+ALTER TABLE users ADD COLUMN notifications_email BOOLEAN NOT NULL DEFAULT true;