Duet stability: packetizer telemetry and recovery notes

[mrmidi]

What changed

• Adds anomaly-only TX packetizer telemetry to the existing driver/MCP log ring: absolute cursor, alignment state/epoch, last DATA packet range, and preparation counters.
• Retains the first CoreAudio range that exceeds the exposed packet timeline, so an incident can be tied to the packetizer state at the transition.
• Publishes the selected stream mode from the audio nub to the AudioDriver configuration path.
• Adds the AV/C recovery and duplex-SYT incident/design document, including the observed corrupt-then-self-rejoining Duet behavior.
• Updates the ASFW MCP control-plane skill with a safe active-audio query workflow.

Why

Duet can continue to transmit isochronous packets with healthy DMA margins and advancing SYT/ZTS while payload frames are dropped because they lie beyond the exposed data timeline. The previous logs could establish underexposure but could not show whether the TX packetizer cursor/alignment had diverged. This PR makes that next transition attributable without adding hot-path logging.

Impact

The telemetry is read-only and anomaly-only at the log-drain level. It does not restart, reconnect, or otherwise manipulate a live stream. The recovery document explicitly distinguishes transport liveness from audio-content correctness and records the required producer-owned recovery direction.

Validation

• ./build.sh --no-bump completed successfully (Debug).
• git diff --check passed.
• Focused host tests were added but could not run in this environment because cmake is not installed.

No driver install, reload, or hardware action was performed.