client: project config and bootstrap

Add Vite + React + TypeScript setup, package.json (react-router-dom,
socket.io-client), global CSS, app entry point and environment
config.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

client/tsconfig.json

@@ -0,0 +1,17 @@
+{
+  "compilerOptions": {
+    "target": "ES2022",
+    "lib": ["ES2023", "DOM", "DOM.Iterable"],
+    "module": "ESNext",
+    "moduleResolution": "bundler",
+    "jsx": "react-jsx",
+    "strict": true,
+    "noEmit": true,
+    "isolatedModules": true,
+    "esModuleInterop": true,
+    "skipLibCheck": true,
+    "forceConsistentCasingInFileNames": true,
+    "types": ["vite/client"]
+  },
+  "include": ["src"]
+}