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/src/main.tsx

@@ -1,13 +1,25 @@
 import { StrictMode } from 'react'
 import { createRoot } from 'react-dom/client'
 import { BrowserRouter } from 'react-router-dom'
+import { QueryClient, QueryClientProvider } from '@tanstack/react-query'
 import './index.css'
 import App from './App.tsx'
 
+const queryClient = new QueryClient({
+  defaultOptions: {
+    queries: {
+      staleTime: 5 * 60 * 1000,
+      retry: 1,
+    },
+  },
+})
+
 createRoot(document.getElementById('root')!).render(
   <StrictMode>
-    <BrowserRouter>
-      <App />
-    </BrowserRouter>
+    <QueryClientProvider client={queryClient}>
+      <BrowserRouter>
+        <App />
+      </BrowserRouter>
+    </QueryClientProvider>
   </StrictMode>,
 )