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/migrations/versions/docker_010_swarm_tasks.py

@@ -0,0 +1,30 @@
+"""Docker swarm service tasks column
+
+Adds docker_swarm_services.tasks_json — each service's newest tasks as a
+manager's agent (≥ 1.8.0) reports them: slot, node, desired and current state,
+Swarm's error and message, exit code and time. Lets Steward tell a task Swarm
+replaced from one that crashed, count a service's failures across task
+retries, and say why its last task failed. Additive column; no DROP+recreate.
+
+Revision ID: docker_010_swarm_tasks
+Revises: docker_009_container_logs
+Create Date: 2026-10-06
+"""
+from typing import Sequence, Union
+from alembic import op
+import sqlalchemy as sa
+
+revision: str = "docker_010_swarm_tasks"
+down_revision: Union[str, None] = "docker_009_container_logs"
+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("tasks_json", sa.Text, nullable=False,
+                            server_default="[]"))
+
+
+def downgrade() -> None:
+    op.drop_column("docker_swarm_services", "tasks_json")