0.5.6: show/hide locked tracks + group lock + crop/mask-preview split

- Timeline: new show/hide toggle next to snap; locked tracks (including
  layer, clip, and the new group lock) are filtered from the timeline
  when the toggle is off. Preference lives in localStorage and is
  shared across components via a module-level ref.
- Groups become lockable via the same inline lock toggle. A locked
  group propagates to its children: they behave as effectively locked
  in the timeline and on the stage. Collapse/expand still works on a
  locked group.
- Canvas: layers in locked+hidden tracks render as a 1px outline in
  the layer (or fill) color instead of their full fill, and are
  draggable:false / listening:false. Mask layers keep their dashed
  ghost styling; masks still apply in the preview overlay regardless
  of lock or show state.
- drawSceneFrame gains an optional `{ crop }` option; the mask-preview
  overlay passes the editor's crop toggle through, so the two controls
  are fully independent. Crop changes now also trigger a preview
  redraw via a watcher dep.
- Tests: new suites for show-locked persistence, group lock store
  action, crop option on drawSceneFrame (including mask+crop combos).
  Properties transparent-toggle tests now reset the section prefs
  localStorage so the Appearance section is guaranteed open when the
  panel mounts.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/i18n/messages.ts

@@ -173,6 +173,8 @@ export const en = {
     toggleTimeUnit: 'Toggle time unit',
     snapOn: 'Snapping on (playhead & keyframes snap together)',
     snapOff: 'Snapping off',
+    hideLocked: 'Hide locked tracks',
+    showLocked: 'Show locked tracks',
     stillFrameTooltip: 'Still frame {time} — holds until the next keyframe',
     keyframeTooltip: 'Keyframe {time} — drag to move, right-click for options',
     trimTooltip: '{name} · {duration}s{trims} · Drag edges to trim, double-click to open',