fix(notifications): task titles and agent slugs replace raw UUIDs (#616)

* fix(notifications): task titles and agent slugs replace raw UUIDs

Notification producers interpolated raw task/agent UUIDs into subjects and
bodies ('Task 68e1e4db-... unblocked', 'handed back to 00000000-...-0004').
A tiny notification_text helper (task_display: title-first with a #id8
fallback; agent_display: identity-map slug first, DB lookup fallback) now
feeds every producer: all 13 NotificationService methods, the 7
delivery-service bodies whose subjects were already title-based, the
substitute-PM ad-hoc insert, and the orchestrator/choreographer callers,
which thread the task row's title one call deeper. Fixes the literal
'cell_pm' role string sent as an agent slug in the merge-conflict
notification. Tool-call examples like unblock('<uuid>') keep the raw id on
purpose — agents need it.

* test(notifications): board-review subject assertion matches the humanized format

---------

Co-authored-by: Renn F <rennf93@users.noreply.github.com>

tests/unit/runtime/test_board_dispatch.py

@@ -226,6 +226,7 @@ async def test_ceo_handoff_once_when_board_review_complete() -> None:
 
     svc = AsyncMock()
     task_svc = AsyncMock()
+    task_svc.get.return_value = SimpleNamespace(title="Strategic feature")
     db_ctx, task_ctx = _patch_handoff_db(task_svc)
     with (
         patch.object(orch, "_is_agent_active", return_value=False),
@@ -239,7 +240,7 @@ async def test_ceo_handoff_once_when_board_review_complete() -> None:
 
     task_svc.mark_board_review_complete.assert_awaited_once()
     svc.send_board_review_complete_notification.assert_awaited_once_with(
-        task_id=task_id
+        task_id=task_id, task_title="Strategic feature"
     )
     assert task_id in orch._board_review_ceo_notified