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.

scripts/vercel-build.ts

@@ -0,0 +1,21 @@
+import { execFileSync } from "node:child_process";
+import { mkdir, readFile, writeFile } from "node:fs/promises";
+
+const appDirectory = "apps/web";
+const resultPath = `${appDirectory}/.vercel/react-router-build-result.json`;
+
+execFileSync("pnpm", ["run", "--filter", "web", "build"], {
+  stdio: "inherit",
+});
+
+const result = JSON.parse(await readFile(resultPath, "utf8"));
+
+for (const bundle of Object.values(result.buildManifest.serverBundles)) {
+  bundle.file = `${appDirectory}/${bundle.file}`;
+}
+
+await mkdir(".vercel", { recursive: true });
+await writeFile(
+  ".vercel/react-router-build-result.json",
+  `${JSON.stringify(result, null, 2)}\n`
+);