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/scheduler/package.json

@@ -0,0 +1,27 @@
+{
+  "name": "scheduler",
+  "version": "0.27.0",
+  "description": "Cooperative scheduler for the browser environment.",
+  "repository": {
+    "type": "git",
+    "url": "https://github.com/facebook/react.git",
+    "directory": "packages/scheduler"
+  },
+  "license": "MIT",
+  "keywords": [
+    "react"
+  ],
+  "bugs": {
+    "url": "https://github.com/facebook/react/issues"
+  },
+  "homepage": "https://react.dev/",
+  "files": [
+    "LICENSE",
+    "README.md",
+    "index.js",
+    "index.native.js",
+    "unstable_mock.js",
+    "unstable_post_task.js",
+    "cjs/"
+  ]
+}