Xiaomi MiMo's /v1/models endpoint returns 401 even with a valid API key,
causing hermes doctor to falsely report 'invalid API key'.
Add a `supports_health_check` field to ProviderProfile (default True).
Providers whose /models endpoint doesn't support auth verification can
set it to False. The doctor's dynamic provider discovery now reads this
field instead of hardcoding True.
The xiaomi provider plugin sets supports_health_check=False.
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