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/isFuture.d.ts

@@ -0,0 +1,20 @@
+import type { DateArg } from "./types.js";
+/**
+ * @name isFuture
+ * @category Common Helpers
+ * @summary Is the given date in the future?
+ * @pure false
+ *
+ * @description
+ * Is the given date in the future?
+ *
+ * @param date - The date to check
+ *
+ * @returns The date is in the future
+ *
+ * @example
+ * // If today is 6 October 2014, is 31 December 2014 in the future?
+ * const result = isFuture(new Date(2014, 11, 31))
+ * //=> true
+ */
+export declare function isFuture(date: DateArg<Date> & {}): boolean;