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/getMonth.js

@@ -0,0 +1,30 @@
+import { toDate } from "./toDate.js";
+
+/**
+ * The {@link getMonth} function options.
+ */
+
+/**
+ * @name getMonth
+ * @category Month Helpers
+ * @summary Get the month of the given date.
+ *
+ * @description
+ * Get the month of the given date.
+ *
+ * @param date - The given date
+ * @param options - An object with options
+ *
+ * @returns The month index (0-11)
+ *
+ * @example
+ * // Which month is 29 February 2012?
+ * const result = getMonth(new Date(2012, 1, 29))
+ * //=> 1
+ */
+export function getMonth(date, options) {
+  return toDate(date, options?.in).getMonth();
+}
+
+// Fallback for modularized imports:
+export default getMonth;