refactor(isoch): make transmit queue payload opaque

[mrmidi]

Summary

Replaces the mixed IsochAudioTransport shared contract with the ABI-v5, payload-opaque IsochTxQueue.

• Keeps the existing three-descriptor allocation RPC, payload slab, metadata ring, OHCI descriptor programming, and on-wire behavior unchanged.
• Leaves transport with only opaque packet metadata, queue state, completion stamps, raw host/cycle anchors, and refill signaling.
• Moves AM824/PCM payload telemetry plus replay/SYT/ZTS producer fault detail into Audio/ where those semantics belong.
• Adds boundary, reset-ownership, queue-fault, lifecycle, and audio-side telemetry coverage.

Why

The former TX control block leaked audio/Wire timing and format semantics into the OHCI transport. That made the transport layer depend on content policy and made later device-family fixes unnecessarily risky. The new seam is payload-opaque and lifetime-owned, matching the completed RX boundary.

Compatibility

No descriptor-layout, queue-size, IIG allocation, or wire-behavior change. The IT channel/descriptor path was cross-checked against the local Linux OHCI reference (ohci.c:queue_iso_transmit).

Validation

• ctest --test-dir build/tests_build --output-on-failure — 1,373 passed; six known fixture skips.
• ./build.sh --no-bump — succeeds without warnings or errors.

Hardware follow-up

• Duet: fixed 48 kHz playback/capture, stop/restart, unplug.
• Saffire/DICE: 44.1 kHz playback/capture, cadence/click monitoring, stop/restart, unplug.