v0.6.40 — Structural montage editing — reorder + remove (Spine 2c)

Added

Structural montage editing — reorder + remove (Spine 2c)

• photoMontage/videoMontage rewritten so each shot is a SELF-CONTAINED named beat
  shot-${i} that owns only its own layer's motion (fade-in ∥ Ken Burns ∥ fade-out). Every
  layer now starts at opacity: 0, and adjacent shots overlap by the crossfade via a negative
  gap in the seq — no shot references its neighbour anymore. This makes a shot an
  independent unit you can reorder, drop, or swap by overlay and survive AI regeneration:
  • Reorder — the existing beat order patch (timeline.shot-2.order) re-sorts shots.
  • Remove — a new generic compose verb removeTimeline: ["shot-2"] splices a beat/step
    out of its parent by label; the seq re-accumulates so later shots ripple up and
    label-anchored dependents (clip start, anchored titles) follow. A dropped shot's layer just
    stays invisible (it never fades in).
  • Swap an image — already a plain nodes.<id>.src patch.
• removeTimeline is the structural complement of the timeline retiming patch (parallel to
  removeNodes); an unknown label is reported as an orphan, never a silent drop. See
  docs/guides/regen-contract.md and examples/overlays/montage-restructure.json.
• The montage now opens on a fade-up and closes on a fade-out (symmetric → edit-safe). Note:
  montage timing shifts slightly (shots overlap by the crossfade); the montage has no golden
  snapshot, so this is a behaviour change in the generator output only, not a determinism break.
• Every generated montage tween now carries a stable label (shot-${i}-in/-kb for the
  fade-in / Ken Burns, cross-${i} for a crossfade, shot-${last}-out for the closing fade)
  alongside the shot-${i} beat name, so the motion is fully addressable by an overlay and
  reframe lint reports no unaddressable motion on a montage.