feat(docker): ingest swarm topology + lifecycle events + health/restart alerts

Wires the agent's enriched + swarm payloads through the docker.persist_host_
samples capability:

  * Swarm topology — persist sample["swarm"] into docker_swarm_services /
    docker_swarm_nodes (upsert + prune stale, host-scoped so two managers don't
    clobber). Migration docker_005 adds services.placement_json for the
    task→node placement the agent now reports.
  * Lifecycle events — _derive_events (pure, unit-tested) diffs the newest
    snapshot against stored per-container state: start / stop / die (non-zero
    exit) / oom / health_change → docker_events rows. Skipped on a host's first
    snapshot so the baseline doesn't emit a start per existing container.
  * Alerts — record restart_count (always) and is_healthy (1.0/0.0, only when a
    HEALTHCHECK exists) alongside cpu/mem, under host-scoped resource names;
    METRIC_CATALOG[docker] gains restart_count + is_healthy so they're alertable.

host_agent ingest captures the newest sample's swarm object and threads it to
the capability (now persist_host_docker(session, host, snapshots, swarm=None));
invoked when containers OR swarm are present, under the same SAVEPOINT. Unit
tests cover the event-diff matrix; integration tests cover event derivation
across two snapshots and swarm topology round-trip (incl. placement).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_016Jg27rgypiW2efULXJDtMC

steward/alerts/routes.py

@@ -24,7 +24,9 @@ METRIC_CATALOG: dict[str, list[str]] = {
     "traefik": ["request_rate", "error_rate", "latency_p50_ms", "latency_p95_ms",
                 "latency_p99_ms", "response_bytes_rate", "cert_expiry_days"],
     "unifi":   ["is_up", "latency_ms", "total_clients"],
-    "docker":  ["cpu_pct", "mem_pct"],
+    # restart_count = cumulative restarts (alert on crash-looping); is_healthy =
+    # 1.0 healthy / 0.0 unhealthy from the container HEALTHCHECK (alert on <1).
+    "docker":  ["cpu_pct", "mem_pct", "restart_count", "is_healthy"],
     "host_agent": [
         "cpu_pct", "mem_used_pct", "mem_available_bytes", "swap_used_bytes",
         "disk_used_pct_worst", "load_1m", "load_5m", "load_15m", "uptime_secs",