feat(docker): Swarm task awareness — replaced tasks, service crash loops, last task error

Milestone 465 "Swarm task awareness". Fixes three defects from the live MCP
review #4973:
- #5008 "Swarm task history read as live state"
- #5009 "Crash-loop detection is blind to Swarm services"
- #5011 "Swarm task errors are not captured"

Agent and ingest (agent 1.8.0):
- A manager's agent now reports each service's newest tasks: slot, node,
  desired and current state, Swarm's Err/Message, exit code and time.
- They are stored in docker_swarm_services.tasks_json (migration
  docker_010_swarm_tasks).

Swarm view (pure):
- A task container is "replaced" when Swarm set its task's desired state off
  `running`. Without the task on record, a newer or running task in the same
  slot decides.
- Replaced containers are no longer replicas or crashes.
- Each service gets, from the task records:
  - failures_1h and failures_24h (failed or rejected tasks);
  - crash_looping (Settings → Thresholds count);
  - last_error, in Swarm's own words.

MCP:
- New findings: swarm_service_crash_looping (critical) and swarm_task_failed
  (warning, on a healthy service with a failure in 24h).
- Down and degraded findings name the last task error.
- list_swarm_services carries the failure fields.
- Container rows mark swarm_replaced and give a replaced task no problems.

Web:
- The containers page swarm cards and the Swarm topology page show crash
  loops, recent failures and the last task error.
- The dashboard widget flags a crash loop, and its "failed (24h)" count no
  longer counts a rolling update's killed task.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

plugins/docker/models.py

@@ -223,6 +223,11 @@ class DockerSwarmService(Base):
     # A manager sees every task, so this captures cross-node placement that the
     # local docker_containers rows (this host only) can't.
     placement_json: Mapped[str] = mapped_column(Text, nullable=False, default="[]")
+    # The service's newest tasks, newest first, as the manager's agent shaped
+    # them: [{"task_id", "slot", "node_id", "desired_state", "state", "message",
+    # "error", "exit_code", "at"}], JSON. Swarm's own record of which tasks it
+    # replaced and why each one stopped; "[]" from agents older than 1.8.0.
+    tasks_json: Mapped[str] = mapped_column(Text, nullable=False, default="[]")
     updated_at: Mapped[datetime] = mapped_column(
         DateTime(timezone=True), nullable=False,
         default=lambda: datetime.now(timezone.utc),