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

plugins/docker/migrations/versions/docker_005_swarm_placement.py

@@ -0,0 +1,29 @@
+"""Docker swarm service placement column
+
+Adds docker_swarm_services.placement_json — the task→node placement of a
+service's running replicas, captured from the agent's swarm payload (a manager
+sees every task, so this records cross-node placement the local container rows
+can't). Additive column; no DROP+recreate.
+
+Revision ID: docker_005_swarm_placement
+Revises: docker_004_events_swarm
+Create Date: 2026-06-19
+"""
+from typing import Sequence, Union
+from alembic import op
+import sqlalchemy as sa
+
+revision: str = "docker_005_swarm_placement"
+down_revision: Union[str, None] = "docker_004_events_swarm"
+branch_labels: Union[str, Sequence[str], None] = None
+depends_on: Union[str, Sequence[str], None] = None
+
+
+def upgrade() -> None:
+    op.add_column("docker_swarm_services",
+                  sa.Column("placement_json", sa.Text, nullable=False,
+                            server_default="[]"))
+
+
+def downgrade() -> None:
+    op.drop_column("docker_swarm_services", "placement_json")