Update README and package.json: add build and test badges to README for CI visibility, and specify pnpm as the package manager in package.json for consistency in dependency management.

frontend/package.json

@@ -3,6 +3,7 @@
   "private": true,
   "version": "0.0.0",
   "type": "module",
+  "packageManager": "pnpm@11.9.0",
   "scripts": {
     "dev": "vite",
     "build": "tsc -b && vite build",