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/minutesToMilliseconds.js

@@ -0,0 +1,25 @@
+import { millisecondsInMinute } from "./constants.js";
+
+/**
+ * @name minutesToMilliseconds
+ * @category Conversion Helpers
+ * @summary Convert minutes to milliseconds.
+ *
+ * @description
+ * Convert a number of minutes to a full number of milliseconds.
+ *
+ * @param minutes - The number of minutes to be converted
+ *
+ * @returns The number of minutes converted in milliseconds
+ *
+ * @example
+ * // Convert 2 minutes to milliseconds
+ * const result = minutesToMilliseconds(2)
+ * //=> 120000
+ */
+export function minutesToMilliseconds(minutes) {
+  return Math.trunc(minutes * millisecondsInMinute);
+}
+
+// Fallback for modularized imports:
+export default minutesToMilliseconds;