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/@babel/traverse/README.md

@@ -0,0 +1,19 @@
+# @babel/traverse
+
+> The Babel Traverse module maintains the overall tree state, and is responsible for replacing, removing, and adding nodes
+
+See our website [@babel/traverse](https://babeljs.io/docs/babel-traverse) for more information or the [issues](https://github.com/babel/babel/issues?utf8=%E2%9C%93&q=is%3Aissue+label%3A%22pkg%3A%20traverse%22+is%3Aopen) associated with this package.
+
+## Install
+
+Using npm:
+
+```sh
+npm install --save-dev @babel/traverse
+```
+
+or using yarn:
+
+```sh
+yarn add @babel/traverse --dev
+```