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/isThisSecond.js

@@ -0,0 +1,28 @@
+import { constructNow } from "./constructNow.js";
+import { isSameSecond } from "./isSameSecond.js";
+
+/**
+ * @name isThisSecond
+ * @category Second Helpers
+ * @summary Is the given date in the same second as the current date?
+ * @pure false
+ *
+ * @description
+ * Is the given date in the same second as the current date?
+ *
+ * @param date - The date to check
+ *
+ * @returns The date is in this second
+ *
+ * @example
+ * // If now is 25 September 2014 18:30:15.500,
+ * // is 25 September 2014 18:30:15.000 in this second?
+ * const result = isThisSecond(new Date(2014, 8, 25, 18, 30, 15))
+ * //=> true
+ */
+export function isThisSecond(date) {
+  return isSameSecond(date, constructNow(date));
+}
+
+// Fallback for modularized imports:
+export default isThisSecond;