feat(docker): schema for lifecycle events + swarm topology

Adds the milestone-77 storage that doesn't fit on the per-container row:

  * docker_events — lifecycle (start/stop/die/oom/health_change), to be
    derived by diffing consecutive host snapshots; host-scoped, indexed for
    timeline lookups (host_id, container_name, at) and retention pruning (at).
  * docker_swarm_services / docker_swarm_nodes — manager-reported Swarm
    topology (desired-vs-running replicas, node role/availability/status).

Migration docker_004 extends the docker branch (down_revision docker_003);
purely additive, no DROP+recreate. event/mode/role are plain strings (no
CHECK whitelist), matching how docker_containers models status. Integration
guard asserts the three new host-scoped tables exist.

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

plugins/docker/models.py

@@ -85,3 +85,89 @@ class DockerMetric(Base):
         Index("ix_docker_metrics_host_container_time",
               "host_id", "container_name", "scraped_at"),
     )
+
+
+class DockerEvent(Base):
+    """Lifecycle events derived by diffing consecutive host snapshots.
+
+    The agent only reports current state, so Steward synthesises lifecycle by
+    comparing each new snapshot against the stored DockerContainer state for the
+    host: a container that appears → `start`; one that vanishes → `stop`; a
+    transition to a stopped status with a non-zero exit → `die`; an OOM-kill
+    flip → `oom`; a health status change → `health_change`. Scoped to the
+    reporting host (names are only unique within a host). `event` is a plain
+    string (no CHECK whitelist), matching how `status` is modelled on
+    DockerContainer — keeps the value set open without a migration per addition.
+    """
+    __tablename__ = "docker_events"
+
+    id: Mapped[str] = mapped_column(
+        String(36), primary_key=True, default=lambda: str(uuid.uuid4())
+    )
+    host_id: Mapped[str] = mapped_column(
+        String(36), ForeignKey("hosts.id", ondelete="CASCADE"), nullable=False
+    )
+    container_name: Mapped[str] = mapped_column(String(255), nullable=False)
+    event: Mapped[str] = mapped_column(String(16), nullable=False)
+    # start | stop | die | oom | health_change
+    detail: Mapped[str | None] = mapped_column(String(255), nullable=True)
+    # e.g. "exit 137", "healthy→unhealthy", image on start
+    at: Mapped[datetime] = mapped_column(
+        DateTime(timezone=True), nullable=False,
+        default=lambda: datetime.now(timezone.utc),
+    )
+
+    # Timeline lookups filter on (host_id, container_name) and sort by time;
+    # retention prunes by `at` alone — index both access paths.
+    __table_args__ = (
+        Index("ix_docker_events_host_container_time",
+              "host_id", "container_name", "at"),
+        Index("ix_docker_events_at", "at"),
+    )
+
+
+class DockerSwarmService(Base):
+    """A Swarm service as seen by a manager host: desired vs running replicas.
+
+    Manager-scoped — only a host that is a Swarm manager reports these, so a
+    single-manager cluster yields one row set keyed by that host. Service names
+    are unique within a swarm; we still key by (host_id, service_name) so two
+    managers reporting independently don't collide.
+    """
+    __tablename__ = "docker_swarm_services"
+
+    host_id: Mapped[str] = mapped_column(
+        String(36), ForeignKey("hosts.id", ondelete="CASCADE"), primary_key=True
+    )
+    service_name: Mapped[str] = mapped_column(String(255), primary_key=True)
+    mode: Mapped[str] = mapped_column(String(16), nullable=False, default="replicated")
+    # replicated | global
+    desired: Mapped[int] = mapped_column(Integer, nullable=False, default=0)
+    running: Mapped[int] = mapped_column(Integer, nullable=False, default=0)
+    image: Mapped[str | None] = mapped_column(String(512), nullable=True)
+    updated_at: Mapped[datetime] = mapped_column(
+        DateTime(timezone=True), nullable=False,
+        default=lambda: datetime.now(timezone.utc),
+    )
+
+
+class DockerSwarmNode(Base):
+    """A Swarm node as seen by a manager host: role / availability / status."""
+    __tablename__ = "docker_swarm_nodes"
+
+    host_id: Mapped[str] = mapped_column(
+        String(36), ForeignKey("hosts.id", ondelete="CASCADE"), primary_key=True
+    )
+    node_id: Mapped[str] = mapped_column(String(64), primary_key=True)
+    hostname: Mapped[str] = mapped_column(String(255), nullable=False, default="")
+    role: Mapped[str] = mapped_column(String(16), nullable=False, default="worker")
+    # manager | worker
+    availability: Mapped[str] = mapped_column(String(16), nullable=False, default="active")
+    # active | pause | drain
+    status: Mapped[str] = mapped_column(String(16), nullable=False, default="unknown")
+    # ready | down | unknown
+    leader: Mapped[bool] = mapped_column(Boolean, nullable=False, default=False)
+    updated_at: Mapped[datetime] = mapped_column(
+        DateTime(timezone=True), nullable=False,
+        default=lambda: datetime.now(timezone.utc),
+    )