Add frontend API client and TanStack Query hooks

Install @tanstack/react-query, create a fetch-based API client with typed
functions for all endpoints, and add query/mutation hooks for games, pokemon,
runs, and encounters. Includes Vite dev proxy for /api and QueryClientProvider
setup.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

frontend/package.json

@@ -10,6 +10,7 @@
     "preview": "vite preview"
   },
   "dependencies": {
+    "@tanstack/react-query": "^5.90.20",
     "react": "^19.2.0",
     "react-dom": "^19.2.0",
     "react-router-dom": "^7.13.0"