- clip-level loop mode (off/loop/clamp), undoable
- per-channel audio levels as one-frame RMS at a timestamp
- waveform min/max buckets over a footage range, rendered on demand
- two real fixes uncovered by this family: conform completion signals
were starved by msleep-only waits (audio renders always came back
empty), and incomplete tickets from conform-pending renders are now
retried until the conform is ready
