v0.0.6-alpha: Perform paving and undo gesture grouping

Architecture paving for the Perform workspace plus a dogfood-driven undo fix. No new user-facing features; Arrange behaves identically with one bug fixed.

• Project Tracks separated from Timeline Content (#68): shared track/channel/device/mixer state now lives in ProjectTracksState addressed by stable TrackId; Arrange owns a separate copy-on-write timeline holding only clips, note clips, and automation. Legacy projects load and re-save unchanged. First seam of the Perform architecture plan.
• Continuous edits group into one undo step (#69): EQ band, knob, fader, and timeline clip drags now collapse into one undo step per pointer gesture.
• Interaction paving (#67): DoubleClick and LocalDrag primitives, per-workspace view modules, theme-aware waveform caches.

Full changes: v0.0.5-alpha...v0.0.6-alpha

What's Changed

• refactor(ui): interaction primitives and shell split (paving for Performance View) by @alexanderwanyoike in #67
• refactor(ui): separate project tracks from timeline content by @alexanderwanyoike in #68
• fix(ui): group continuous edits into one undo step by @alexanderwanyoike in #69
• Release v0.0.6-alpha: Perform paving and undo gesture grouping by @alexanderwanyoike in #70

Full Changelog: v0.0.5-alpha...v0.0.6-alpha