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/package.json

@@ -0,0 +1,26 @@
+{
+  "name": "calendarapi-frontend",
+  "private": true,
+  "version": "1.0.0",
+  "type": "module",
+  "scripts": {
+    "dev": "vite",
+    "build": "tsc -b && vite build",
+    "preview": "vite preview"
+  },
+  "dependencies": {
+    "date-fns": "^4.1.0",
+    "react": "^19.0.0",
+    "react-dom": "^19.0.0",
+    "react-router-dom": "^7.2.0"
+  },
+  "devDependencies": {
+    "@tailwindcss/vite": "^4.0.0",
+    "@types/react": "^19.0.0",
+    "@types/react-dom": "^19.0.0",
+    "@vitejs/plugin-react": "^4.3.0",
+    "tailwindcss": "^4.0.0",
+    "typescript": "~5.7.0",
+    "vite": "^6.2.0"
+  }
+}