add server api handlers. Fix bug with cmd output

README.md

@@ -53,6 +53,37 @@ stays local to the client config.
 - Client behavior notes: [docs/client.md](docs/client.md)
 - Server behavior notes: [docs/server.md](docs/server.md)
 
+## Server API
+
+The server uses SQLite through SQLAlchemy by default:
+
+```bash
+NEXUS_SYNC_DATABASE_URL="sqlite:///nexus-sync.db"
+```
+
+Useful server-side handlers:
+
+```text
+POST /api/v1/client/heartbeat
+GET  /api/v1/server/clients
+GET  /api/v1/server/clients/{client_id}
+POST /api/v1/server/clients/{client_id}/commands
+GET  /api/v1/server/commands/{command_id}
+```
+
+Queue command example:
+
+```json
+{
+  "name": "hostname",
+  "args": {},
+  "timeout_seconds": 30
+}
+```
+
+Clients receive queued commands on their next heartbeat and report results in a
+later heartbeat.
+
 ### To build
 
 ```