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/buildFormatLongFn.d.cts

@@ -0,0 +1,14 @@
+import type { FormatLongFn, FormatLongWidth } from "../types.js";
+export interface BuildFormatLongFnArgs<
+  DefaultMatchWidth extends FormatLongWidth,
+> {
+  formats: Partial<{
+    [format in FormatLongWidth]: string;
+  }> & {
+    [format in DefaultMatchWidth]: string;
+  };
+  defaultWidth: DefaultMatchWidth;
+}
+export declare function buildFormatLongFn<
+  DefaultMatchWidth extends FormatLongWidth,
+>(args: BuildFormatLongFnArgs<DefaultMatchWidth>): FormatLongFn;