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/isEqual.js

@@ -0,0 +1,29 @@
+import { toDate } from "./toDate.js";
+
+/**
+ * @name isEqual
+ * @category Common Helpers
+ * @summary Are the given dates equal?
+ *
+ * @description
+ * Are the given dates equal?
+ *
+ * @param dateLeft - The first date to compare
+ * @param dateRight - The second date to compare
+ *
+ * @returns The dates are equal
+ *
+ * @example
+ * // Are 2 July 2014 06:30:45.000 and 2 July 2014 06:30:45.500 equal?
+ * const result = isEqual(
+ *   new Date(2014, 6, 2, 6, 30, 45, 0),
+ *   new Date(2014, 6, 2, 6, 30, 45, 500)
+ * )
+ * //=> false
+ */
+export function isEqual(leftDate, rightDate) {
+  return +toDate(leftDate) === +toDate(rightDate);
+}
+
+// Fallback for modularized imports:
+export default isEqual;