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>

app/backend/sqlc/queries/agents.sql

@@ -29,6 +29,7 @@ UPDATE node_agents SET
     last_heartbeat = $10,
     metadata = $11,
     auto_prune = $12,
+    schedulable = $13,
     updated_at = NOW()
 WHERE id = $1
 RETURNING *;
@@ -113,3 +114,37 @@ WHERE id = $1;
 SELECT * FROM agent_commands
 WHERE node_agent_id = $1 AND type = $2
 ORDER BY created_at DESC LIMIT 1;
+
+-- name: PickLeastLoadedAgent :one
+SELECT a.id FROM node_agents a
+LEFT JOIN LATERAL (
+    SELECT h.container_count FROM agent_heartbeats h
+    WHERE h.node_agent_id = a.id
+    ORDER BY h.timestamp DESC LIMIT 1
+) h ON true
+WHERE a.status = 'online' AND a.schedulable
+ORDER BY COALESCE(h.container_count, 0) ASC, a.created_at ASC
+LIMIT 1;
+
+-- name: SetAgentSchedulable :exec
+UPDATE node_agents SET schedulable = $2, updated_at = NOW() WHERE id = $1;
+
+-- name: ClearServiceNodePins :execrows
+UPDATE services SET node_id = NULL, updated_at = NOW() WHERE node_id = $1;
+
+-- name: UpsertServiceContainer :exec
+INSERT INTO container_instances (
+    id, name, image, project_id, service_id, node_agent_id,
+    status, resources, ports, environment, volumes, networks,
+    restart_policy, health_check
+) VALUES ($1, $2, $3, $4, $5, $6, $7, $8, $9, $10, $11, $12, $13, $14)
+ON CONFLICT (id) DO UPDATE SET
+    image = EXCLUDED.image,
+    status = EXCLUDED.status,
+    updated_at = NOW();
+
+-- name: DeleteServiceContainersOnAgent :exec
+DELETE FROM container_instances WHERE node_agent_id = $1 AND service_id = $2;
+
+-- name: ScrubCommandPayload :exec
+UPDATE agent_commands SET payload = $2, updated_at = NOW() WHERE id = $1;