Let pipeline subprocess stderr flow to uvicorn terminal

Removed stderr=subprocess.DEVNULL from POST /api/tasks/{id}/run
so errors from background kin run are visible in the API server log.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

web/api.py

@@ -236,7 +236,6 @@ def run_task(task_id: str):
          str(DB_PATH)],
         cwd=str(kin_root),
         stdout=subprocess.DEVNULL,
-        stderr=subprocess.DEVNULL,
     )
     return JSONResponse({"status": "started", "task_id": task_id}, status_code=202)