feat: add graceful shutdown endpoint for UVM API server and update documentation

README.md

@@ -303,6 +303,7 @@ The server exposes these routes:
 | `GET` | `/` | Redirect to the local dashboard |
 | `GET` | `/dashboard` | Serve the local management dashboard |
 | `GET` | `/health` | Unauthenticated liveness response |
+| `POST` | `/exit` | Gracefully stop the UVM API server |
 | `GET` | `/diagnostics` | Run host readiness checks for the dashboard/system view |
 | `POST` | `/install` | Install or refresh host assets; body: `{ "force": false }` |
 | `GET` | `/vms` | List VM records and observed status |
@@ -364,6 +365,18 @@ curl \
   http://127.0.0.1:8000/vms
 ```
 
+Stop the API server without stopping its managed VMs:
+
+```sh
+curl -X POST \
+  -H "X-UVM-Token: $UVM_API_TOKEN" \
+  http://127.0.0.1:8000/exit
+```
+
+The endpoint returns `202 {"status":"stopping"}` and then gracefully terminates
+the UVM API process. It is a protected management endpoint; it does not stop or
+delete managed VMs.
+
 Do not expose this server directly to an untrusted network. For remote access,
 keep TLS enabled and consider placing it behind an additional authenticated
 reverse proxy.