The /api/transcribe/capability probe's resolve_provider() only knew the
built-in STT providers, so an explicit stt.provider mapping to a Hermes
command-type provider was reported unavailable and the browser fell back
unnecessarily. Add command_provider_available(), delegating to the agent's
_resolve_command_stt_provider_config(provider, cfg) as the single source of
truth, consulted as the final fallthrough after the built-in chain (the
agent rejects built-in names internally, so ordering can't shadow a native
provider). Added a clarifying comment that command providers are
intentionally omitted from the auto-detect tuple to match the agent's
_get_provider() precedence.
Co-authored-by: LLMinem <LLMinem@users.noreply.github.com>
