Only mention the hermes-agent-setup skill in STT failure notes (both
the direct user message and the agent context note) when the skill is
actually installed. Uses _find_skill() from skill_manager_tool.
Also confirmed: STT is the only user-facing failure case where the
setup skill hint helps. Vision failures are transient API issues,
runtime transcription errors indicate a configured-but-broken provider,
and platform startup warnings are server logs.
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