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.

.dockerignore

@@ -0,0 +1,35 @@
+# Repo-wide ignore for the agents/runner Docker builds.
+# Keeps images small and prevents secrets from entering image layers.
+
+node_modules
+**/node_modules
+**/dist
+**/.flue-vite
+
+# Secrets — never bake into an image.
+.env
+.env.*
+!.env.example
+**/.env
+**/.env.*
+
+# Local Convex / runtime state.
+.convex
+**/.convex
+data
+**/data
+
+# VCS, caches, and editor cruft.
+.git
+.gitignore
+**/.DS_Store
+**/.vscode
+**/.idea
+
+# macOS AppleDouble sidecars are metadata, never TypeScript source.
+**/._*
+
+# Workspaces and runner artifacts created at runtime on the host.
+workspaces
+**/workspaces
+*.log