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/app_controller.py

@@ -2120,6 +2120,12 @@ class AppController:
   """
   return self._warmup.status()
 
+ def warmup_canaries(self) -> list[dict]:
+  """
+   Per-module import canary records. Each record carries: canary_id, module, thread_name, thread_id, submit_ts, start_ts, end_ts, elapsed_ms, status, error. Useful for debugging which worker thread loaded which module and how long it took. Returns a defensive copy (caller mutation is safe). [SDM: src/app_controller.py:warmup_canaries].
+  """
+  return self._warmup.canaries()
+
  def is_warmup_done(self) -> bool:
   """