0.18.2: centre crosshair + locked-track selection + eye-on-lock

- Optional centre crosshair: dashed horizontal + vertical lines
  through the effective canvas centre, togglable from the HUD next
  to the crop / mask-preview / stage-preview buttons. Scales with
  zoom and stays visible inside clip-edit.
- Locked clip tracks now behave as if they weren't on the stage —
  the ci-group is listening:false + draggable:false, so selection,
  drag, and transform all pass through. deselectIfLocked also
  clears a clip-instance selection that just got locked out
  (directly or via a parent group).
- Eye toggle stays clickable on locked layer / clip-track rows —
  previous pointer-events:none rule only whitelisted the lock
  button. Hide-in-editor is orthogonal to lock.

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

src/i18n/messages.ts

@@ -324,6 +324,8 @@ export const en = {
     maskPreviewOff: 'Back to edit view',
     stagePreviewOn: 'Turn stage preview on — buttons become interactive',
     stagePreviewOff: 'Turn stage preview off — buttons behave as normal assets',
+    centerCrosshairOn: 'Show centre crosshair',
+    centerCrosshairOff: 'Hide centre crosshair',
     vertexCorner: 'Corner',
     vertexCurve: 'Curve (smooth)',
     vertexSplitCurve: 'Split curve',