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/jiti/lib/jiti.d.cts

@@ -0,0 +1,8 @@
+import * as types from "./types.js";
+declare const allExports: typeof types & {
+  /**
+   * @deprecated Please use `const { createJiti } = require("jiti")` or use ESM import.
+   */
+  (...args: Parameters<typeof types.createJiti>): types.Jiti;
+};
+export = allExports;