feat(web): vercel deployment and vds compose/systemd setup

Add Vercel config with React Router preset, vercel-build script and
/api/auth rewrite to the Convex site. Add VDS staging compose for the
Rivet engine and runner plus systemd units, deployment plan, and
Docker/Vercel ignore rules. Lockfile covers both the web and agents
dependency additions.

apps/web/package.json

@@ -35,6 +35,7 @@
     "@types/node": "catalog:",
     "@types/react": "catalog:",
     "@types/react-dom": "catalog:",
+    "@vercel/react-router": "1.3.1",
     "react-router-devtools": "^6.2.1",
     "tailwindcss": "catalog:",
     "typescript": "catalog:",