v0.22.0 — music-only waveform fix + per-channel Split Channels

See the music, not the timecode, in every waveform.

• Bug fix: for a file with LTC striped on its own channel, the Edit Media sheet's preview was still drawing the LTC channel (the main preview-pane waveform already excluded it). Now no waveform surface shows the timecode buzz — the Edit Media preview excludes the detected LTC channel too.
• New: View ▸ Split Channels (opt-in, off by default). When on, the waveform draws one lane per music channel so you can read left/right separately in stereo music. The detected LTC channel is kept out of the lanes and named in the badge instead — e.g. R = LTC (muted) · 01:00:00:00.
• The playhead, cue markers, tempo grid, click-to-seek and lyrics span all lanes. With the toggle off, existing waveforms render exactly as before (full height, no change).

Implements #720. Builds on v0.20.0's music-only source audio.

Notes: ad-hoc signed (free-tier) — first launch: right-click → Open, or xattr -dr com.apple.quarantine /Applications/OnlyCue.app. The split-channel rendering and the striped-file check were verified by code review + unit tests (1409, 0 failures); the on-device UI-automation run is pending a runner-environment fix.