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/getRoundingMethod.cjs

@@ -0,0 +1,11 @@
+"use strict";
+exports.getRoundingMethod = getRoundingMethod;
+
+function getRoundingMethod(method) {
+  return (number) => {
+    const round = method ? Math[method] : Math.trunc;
+    const result = round(number);
+    // Prevent negative zero
+    return result === 0 ? 0 : result;
+  };
+}