#3438 [Benchmark] bench run stop_engine: taskkill result unchecked and wait timeout discarded, a failed engine kill is silent

Descrição

`strata_cli/bench_standard.py` at v0.2.1 (commit 90767252), `stop_engine`
(around lines 697-720):

```python
if os.name == "nt":
    subprocess.run(["taskkill", "/PID", str(proc.pid), "/T", "/F"], capture_output=True, timeout=60)
...
try:
    proc.wait(30)
except subprocess.TimeoutExpired:
    pass
```

The taskkill return code and output are never checked and the wait timeout is
discarded, so a denied or failed kill produces no message. On my run
(2026-10-20, run id 20261020T105417Z-5b4dbf77) the engine start came up in a
state that denied the kill (Access is denied, likely an elevated or stuck
tree), and the runner reported a normal finish while two python processes kept
port 8080 until a manual elevated taskkill. Five freshly started engines on
the same machine died to the first taskkill, so the unchecked result is the
defect; my denied kill was the trigger.

Related, same artifact: the run folder's `engine.log` is 0 bytes by design on
this path, because the serve layer writes to the run config's own log file and
the runner's capture records nothing. Consider pointing the artifact at the
config log path, or noting in the protocol that engine.log can be empty on
Windows.

Reproduction status: one occurrence in one run. Environment: Windows 10 build
19044, source checkout at v0.2.1, RX 7900 XTX, engine 0.1.45.