feat(ansible): runner robustness — cancel, concurrency, structured results, retention

Closes #550 (all four):

- Cancellation: track live subprocesses; POST /ansible/runs/<id>/cancel
  (operator) SIGTERMs then SIGKILLs after a grace; new 'cancelled' status
  (+ migration 0019, ALTER TYPE in autocommit). Queued runs cancel cleanly
  before launch. Cancel button on run detail.
- Concurrency: global semaphore (ansible.max_concurrent_runs, default 3,
  Settings→Ansible) caps simultaneous runs; excess show 'queued' (new status)
  until a slot frees. Semaphore bound lazily per running loop.
- Structured results: parse PLAY RECAP into per-host ok/changed/unreachable/
  failed/skipped + capture failed-task lines, stored in new results JSON
  column (migration 0020); rendered as a host-summary table on run detail.
  Keeps live streaming (no json-callback swap).
- Retention: full output written to a persistent log artifact
  (/data/ansible/runs/<id>.log, env-overridable) beyond the 1 MB DB cap and
  across restarts; in-memory replay buffer bounded + GC'd after completion;
  Download-log route. Boot reconciliation now also sweeps stale 'queued'.

Unit tests for recap parsing + cancel flagging. Status colors updated across
run list / detail / schedules.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

steward/migrations/versions/0020_ansible_run_results.py

@@ -0,0 +1,22 @@
+"""Add results JSON column to ansible_runs (parsed per-host summary)
+
+Revision ID: 0020_ansible_run_results
+Revises: 0019_ansible_run_statuses
+Create Date: 2026-06-16
+"""
+from typing import Sequence, Union
+from alembic import op
+import sqlalchemy as sa
+
+revision: str = "0020_ansible_run_results"
+down_revision: Union[str, None] = "0019_ansible_run_statuses"
+branch_labels: Union[str, Sequence[str], None] = None
+depends_on: Union[str, Sequence[str], None] = None
+
+
+def upgrade() -> None:
+    op.add_column("ansible_runs", sa.Column("results", sa.JSON(), nullable=True))
+
+
+def downgrade() -> None:
+    op.drop_column("ansible_runs", "results")