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/plugin-transform-react-jsx-source/README.md

@@ -0,0 +1,19 @@
+# @babel/plugin-transform-react-jsx-source
+
+> Add a __source prop to all JSX Elements
+
+See our website [@babel/plugin-transform-react-jsx-source](https://babeljs.io/docs/babel-plugin-transform-react-jsx-source) for more information.
+
+## Install
+
+Using npm:
+
+```sh
+npm install --save-dev @babel/plugin-transform-react-jsx-source
+```
+
+or using yarn:
+
+```sh
+yarn add @babel/plugin-transform-react-jsx-source --dev
+```