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/react-dom/cjs/react-dom-test-utils.production.js

@@ -0,0 +1,21 @@
+/**
+ * @license React
+ * react-dom-test-utils.production.js
+ *
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+"use strict";
+var React = require("react"),
+  didWarnAboutUsingAct = !1;
+exports.act = function (callback) {
+  !1 === didWarnAboutUsingAct &&
+    ((didWarnAboutUsingAct = !0),
+    console.error(
+      "`ReactDOMTestUtils.act` is deprecated in favor of `React.act`. Import `act` from `react` instead of `react-dom/test-utils`. See https://react.dev/warnings/react-dom-test-utils for more info."
+    ));
+  return React.act(callback);
+};