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/README.md

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+# `react`
+
+React is a JavaScript library for creating user interfaces.
+
+The `react` package contains only the functionality necessary to define React components. It is typically used together with a React renderer like `react-dom` for the web, or `react-native` for the native environments.
+
+**Note:** by default, React will be in development mode. The development version includes extra warnings about common mistakes, whereas the production version includes extra performance optimizations and strips all error messages. Don't forget to use the [production build](https://reactjs.org/docs/optimizing-performance.html#use-the-production-build) when deploying your application.
+
+## Usage
+
+```js
+import { useState } from 'react';
+import { createRoot } from 'react-dom/client';
+
+function Counter() {
+  const [count, setCount] = useState(0);
+  return (
+    <>
+      <h1>{count}</h1>
+      <button onClick={() => setCount(count + 1)}>
+        Increment
+      </button>
+    </>
+  );
+}
+
+const root = createRoot(document.getElementById('root'));
+root.render(<Counter />);
+```
+
+## Documentation
+
+See https://react.dev/
+
+## API
+
+See https://react.dev/reference/react