fix(api): default event loop to asyncio + cancellation-safe commit — kills the CI segfault (#340)

* fix(api): default the event loop to asyncio + cancellation-safe commit

The recurring CI e2e segfault traced to uvloop: the harness's
uvicorn.run() auto-selected it while production's serve() path never
consulted Config.loop (stock asyncio, accidentally safe). Every launch
site now resolves ROBOCO_UVICORN_LOOP (default asyncio; uvloop opt-in),
and DbCommitMiddleware's commit-in-send can no longer be interrupted
mid-wire: on cancellation it gets a bounded grace to finish (committed
data survives the 504), else invalidate-and-reraise.

* feat(runtime): expected-stop breadcrumbs attribute container deaths

Two production exit-143s had no attributable source: every orchestrator
kill path now records a short reason breadcrumb, and the exit monitor
consumes it -- an expected stop logs its reason at info, a genuinely
unexpected one logs none_recorded plus docker-inspect diagnostics
(OOMKilled, timestamps) so the next mystery SIGTERM self-identifies.

---------

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

tests/unit/runtime/test_gateway_health.py

@@ -121,7 +121,9 @@ async def test_broken_past_grace_is_killed(monkeypatch: pytest.MonkeyPatch) -> N
     monkeypatch.setattr(orch, "_remove_container", remove)
     monkeypatch.setattr(orch, "_probe_gateway_health", AsyncMock(return_value=False))
     assert await orch._maybe_recover_broken_gateway(_task()) is True
-    remove.assert_awaited_once_with("roboco-agent-be-dev-1")
+    remove.assert_awaited_once_with(
+        "roboco-agent-be-dev-1", stop_reason="gateway_health_recovery"
+    )
     assert "be-dev-1" not in orch._instances  # evicted