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/fp/_lib/convertToFP.js

@@ -0,0 +1,17 @@
+/**
+ * Converts a function to a curried function that accepts arguments in reverse
+ * order.
+ *
+ * @param fn - The function to convert to FP
+ * @param arity - The arity of the function
+ * @param curriedArgs - The curried arguments
+ *
+ * @returns FP version of the function
+ *
+ * @private
+ */
+export function convertToFP(fn, arity, curriedArgs = []) {
+  return curriedArgs.length >= arity
+    ? fn(...curriedArgs.slice(0, arity).reverse())
+    : (...args) => convertToFP(fn, arity, curriedArgs.concat(args));
+}