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/isLastDayOfMonth.js

@@ -0,0 +1,29 @@
+import { endOfDay } from "./endOfDay.js";
+import { endOfMonth } from "./endOfMonth.js";
+import { toDate } from "./toDate.js";
+
+/**
+ * @name isLastDayOfMonth
+ * @category Month Helpers
+ * @summary Is the given date the last day of a month?
+ *
+ * @description
+ * Is the given date the last day of a month?
+ *
+ * @param date - The date to check
+ * @param options - An object with options
+ *
+ * @returns The date is the last day of a month
+ *
+ * @example
+ * // Is 28 February 2014 the last day of a month?
+ * const result = isLastDayOfMonth(new Date(2014, 1, 28))
+ * //=> true
+ */
+export function isLastDayOfMonth(date, options) {
+  const _date = toDate(date, options?.in);
+  return +endOfDay(_date, options) === +endOfMonth(_date, options);
+}
+
+// Fallback for modularized imports:
+export default isLastDayOfMonth;