bench: run one server at a time, match thinking mode, fix tools package

Refinements from end-to-end bring-up on the GPU host:

- Run each system start→suites→stop in sequence. Two BF16 8B models don't
  co-reside on one 32GB GPU, and a resident idle engine would distort the
  other's latency/throughput.
- Match generation mode: xserv hardcodes Qwen3 thinking off, so send
  chat_template_kwargs={enable_thinking:false} to llama.cpp via a per-endpoint
  extra_body. --enable-thinking opts back into thinking mode.
- Add tools/__init__.py so `python3 -m tools.bench.runner` resolves our package
  instead of a site-packages `tools` (nvfuser ships one that shadowed it).
- Document offline-GPU-host workflow, thinking-match, and the xserv 8192 OOM
  finding that the bench surfaced.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

tools/bench/quality.py

@@ -81,6 +81,7 @@ async def _run_one_task(
                 temperature=cfg.quality_temperature,
                 api_key=ep.api_key,
                 timeout=cfg.request_timeout_s,
+                extra_body=ep.extra_body,
             )
             pred = task_mod.extract_answer(r.text) if r.error is None else None
             correct = task_mod.score(pred, prob["answer"]) if r.error is None else False