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.

package.json

@@ -69,6 +69,7 @@
     "build:agents": "vp run --filter @code/agents build",
     "docs:update": "node scripts/update-docs.ts",
     "subtree": "node scripts/subtree.ts",
+    "vercel-build": "node scripts/vercel-build.ts",
     "check": "ultracite check --disable-nested-config",
     "fix": "ultracite fix --disable-nested-config"
   },
@@ -80,12 +81,14 @@
     "@flue/sdk": "npm:@rivet-dev/labs-flue-sdk@1.0.0-beta.9-rivet.2",
     "@types/bun": "catalog:",
     "@types/node": "catalog:",
+    "@vercel/config": "^0.5.5",
     "concurrently": "^9.1.2",
     "convex": "catalog:",
     "convex-test": "catalog:",
     "effect": "catalog:",
     "oxfmt": "0.61.0",
     "oxlint": "1.76.0",
+    "react-router": "^8.1.0",
     "rolldown": "1.1.4",
     "typescript": "catalog:",
     "ultracite": "7.9.3",