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/react-dom/static.edge.js

@@ -0,0 +1,12 @@
+'use strict';
+
+var s;
+if (process.env.NODE_ENV === 'production') {
+  s = require('./cjs/react-dom-server.edge.production.js');
+} else {
+  s = require('./cjs/react-dom-server.edge.development.js');
+}
+
+exports.version = s.version;
+exports.prerender = s.prerender;
+exports.resumeAndPrerender = s.resumeAndPrerender;