feat(warmup): per-module canary records (thread + timing observability)

Adds a canary record for each module submitted to the warmup, tracking:
canary_id, module, thread_name, thread_id, submit_ts, start_ts,
end_ts, elapsed_ms, status, error.

Surface:
- WarmupManager.canaries() returns list[dict] (defensive copy)
- AppController.warmup_canaries() returns list[dict] (delegation)
- GET /api/warmup_canaries Hook API endpoint
- ApiHookClient.get_warmup_canaries() returns list[dict]

Example: the warmup of google.genai records a 1187ms canary on
thread controller-io_0 with thread_id 50420, canary_id 1.

11 new tests (8 unit in test_warmup_canaries + 3 in test_api_hooks_warmup).
All pass; live_gui smoke test confirms endpoint returns real data.

src/api_hook_client.py

@@ -318,6 +318,17 @@ class ApiHookClient:
   """
   return self._make_request('GET', f'/api/warmup_wait?timeout={timeout}') or {}
 
+ def get_warmup_canaries(self) -> list[dict[str, Any]]:
+  """
+  Returns per-module import canary records: list of dicts with
+  canary_id, module, thread_name, thread_id, submit_ts, start_ts,
+  end_ts, elapsed_ms, status, error. Used for debugging which
+  worker thread loaded which module and how long it took.
+  [C: tests/test_api_hooks_warmup.py:test_get_warmup_canaries_in_live_gui]
+  """
+  result = self._make_request('GET', '/api/warmup_canaries') or {}
+  return result.get("canaries", []) if isinstance(result, dict) else []
+
 #endregion: Diagnostics
 
 #region: Project