feat: add Vercel deployment config for frontend

- Add vercel.json with Vite framework settings
- Configure SPA rewrites for client-side routing

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

apps/matrix-frontend/vercel.json

@@ -0,0 +1,10 @@
+{
+  "$schema": "https://openapi.vercel.sh/vercel.json",
+  "buildCommand": "npm run build",
+  "outputDirectory": "dist",
+  "installCommand": "npm install",
+  "framework": "vite",
+  "rewrites": [
+    { "source": "/(.*)", "destination": "/index.html" }
+  ]
+}