start_recording now creates the EventSink alongside the existing frame
channel and forwards Level/DeviceChanged onto a small fire-and-forget
thread that emits "recording://level" and "recording://device".
Adds AudioLevel (rms/peak per chunk, throttled to ~20Hz) and
CaptureEvent::DeviceChanged emitted through a new EventSink alongside
the existing FrameSink. On a capture read failure, reopens against
whatever is now the default render device and continues the same WAV
file if the new format is compatible; otherwise fails loudly rather
than silently corrupting the recording.
Reports LLM endpoint/local-only status and enabled sync targets so the
UI can prove local-only handling, per the shape fixed in
docs/04-api-contracts.md. Sync targets stay empty until Phase 9 lands
SyncManager; list_sync_targets' not_implemented error is swallowed
rather than failing the whole self-check.
iamdoubz