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/_lib/normalizeDates.cjs

@@ -0,0 +1,11 @@
+"use strict";
+exports.normalizeDates = normalizeDates;
+var _index = require("../constructFrom.cjs");
+
+function normalizeDates(context, ...dates) {
+  const normalize = _index.constructFrom.bind(
+    null,
+    context || dates.find((date) => typeof date === "object"),
+  );
+  return dates.map(normalize);
+}