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/date-fns/locale/_lib/buildMatchPatternFn.d.cts

@@ -0,0 +1,9 @@
+import type { MatchFn, MatchValueCallback } from "../types.js";
+export interface BuildMatchPatternFnArgs<Result> {
+  matchPattern: RegExp;
+  parsePattern: RegExp;
+  valueCallback?: MatchValueCallback<string, Result>;
+}
+export declare function buildMatchPatternFn<Result>(
+  args: BuildMatchPatternFnArgs<Result>,
+): MatchFn<Result>;