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/api/pokemon.ts

@@ -0,0 +1,6 @@
+import { api } from './client'
+import type { Pokemon } from '../types/game'
+
+export function getPokemon(id: number): Promise<Pokemon> {
+  return api.get(`/pokemon/${id}`)
+}