Summary

Salvage of PR #9720 by @sjz-ks (cherry-picked onto current main). Closes #9716.

Fixes two hermes doctor false-negative bugs for kimi-coding-cn / Moonshot China credentials:

1. Missing env hint: KIMI_CN_API_KEY was not in _PROVIDER_ENV_HINTS, so _has_provider_env_config() returned False for China-only Kimi setups — doctor tells users to run hermes setup even though their key is configured.

2. Null-safety crash: The Kimi China entry in _apikey_providers has base_env=None (correct — no user-configurable base URL override for the China endpoint), but os.getenv(_base_env, "") crashes with TypeError: str expected, not NoneType.

Changes (2 lines of production code)

• Add "KIMI_CN_API_KEY" to _PROVIDER_ENV_HINTS
• Guard: os.getenv(_base_env, "") if _base_env else ""
• 2 regression tests added

Test plan

python -m pytest tests/hermes_cli/test_doctor.py -q → 19 passed