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

frontend/node_modules/lightningcss/node/index.mjs

@@ -0,0 +1,4 @@
+import index from './index.js';
+
+const { transform, transformStyleAttribute, bundle, bundleAsync, browserslistToTargets, composeVisitors, Features } = index;
+export { transform, transformStyleAttribute, bundle, bundleAsync, browserslistToTargets, composeVisitors, Features };