feat(scheduling): multi-node service placement + remote lifecycle (#54)

* feat(scheduling): multi-node service placement + remote container lifecycle

services.node_id pins a service to a node agent: explicit id, "auto"
(least-loaded online node), or "local"/empty for the local Docker host.

- DeploymentEngine gains a NodeRunner seam; ReconcileService routes
  pinned services to the agent's command queue (create_container with
  image/env/command/ports/volumes/labels/resource limits), tracked in
  container_instances with deterministic per-replica ids.
- Stop/start/restart/delete fan out to the pinned node — no more leaked
  remote containers on service delete.
- Agent create_container is idempotent (rm -f first) and honors restart
  policy, labels, memory/cpus, published+ephemeral ports, volumes, env.
- GET /nodes/options exposes id/name/status to authed users; full agent
  management stays admin-only.
- CLI services create/update --node, MCP node_id docs, OpenAPI
  node_id/node_name + /nodes/options, service-detail Placement section.

Ceilings: remote nodes run registry-pulled images only — git builds,
Traefik domains, and remote sleep detection stay local until
build-on-node and per-node ingress land.

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Co-Authored-By: Devin <158243242+devin-ai-integration[bot]@users.noreply.github.com>

* feat(scheduling): node cordon/drain + schedulable gate

- node_agents.schedulable column; "auto" placement and explicit pins skip
  cordoned nodes; already-pinned services keep running (reconcile is
  unaffected — cordon is not eviction).
- POST /agents/:id/cordon|uncordon|drain (admin). Drain cordons, removes
  every service container via the agent queue, and clears the services'
  pins so they redeploy on the local host. Requires the node online —
  an offline node can't acknowledge removals.
- CLI nodes cordon|uncordon|drain (drain confirm-gated), MCP
  containr_nodes_cordon|uncordon|drain, OpenAPI paths + schedulable
  field, node-detail page cordon badge + drain/cordon controls.
- Fix: re-registering an agent no longer resets auto_prune.

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Co-Authored-By: Devin <158243242+devin-ai-integration[bot]@users.noreply.github.com>

* feat(scheduling): remote registry pulls + post-run health check

- Dispatch payload carries the project owner's registry credentials for
  the image host; the agent docker-logins for the pull and logs out
  after, so private images deploy to remote nodes.
- Completed command payloads get their registry password scrubbed —
  secrets don't linger in agent_commands rows.
- Agent verifies the container is still running ~1.5s after docker run;
  crash-loops now fail the deployment with the container's last log
  lines instead of reporting "running" optimistically.

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Co-Authored-By: Devin <158243242+devin-ai-integration[bot]@users.noreply.github.com>

---------

Co-authored-by: Devin <158243242+devin-ai-integration[bot]@users.noreply.github.com>

app/backend/internal/api/deployments.go

@@ -421,6 +421,20 @@ func runDeploymentAndSyncWithImage(
 		maintURL = maintenanceURL(db)
 	}
 
+	// Node-pinned services dispatch to the agent's command queue. Builds run
+	// on the local host, so remote placement only works for registry-pulled
+	// images — git-sourced and rollback deploys fail fast with that message.
+	nodeID := serviceNodeID(db, service.ID)
+	if nodeID != "" && (service.GitRepo != "" || imageOverride != "") {
+		failedAt := time.Now()
+		msg := "service is pinned to a remote node but remote nodes only run registry-pulled images (git builds and rollbacks stay local — build-on-node is not yet supported)"
+		_, _ = db.Exec(
+			`UPDATE deployments SET status = 'failed', error = $1, completed_at = $2, updated_at = $2 WHERE id = $3`,
+			msg, failedAt, dbDeployment.ID,
+		)
+		return
+	}
+
 	deployReq := &deployment.DeploymentRequest{
 		ProjectID:   service.ProjectID.String(),
 		ServiceID:   service.ID.String(),
@@ -447,6 +461,7 @@ func runDeploymentAndSyncWithImage(
 			Maintenance:    maintenanceMode,
 			MaintenanceURL: maintURL,
 			BasicAuthUsers: basicAuthUsers,
+			NodeID:         nodeID,
 		},
 		Trigger: deployment.TriggerConfig{
 			Type:      req.Trigger,