1.1.3: multi-select on the stage — marquee, group transform, panel

- Click-and-drag on the empty stage starts a layer marquee with
  touch (not enclose) semantics — every unlocked layer whose bbox
  overlaps the drag rect joins the selection. Tiny clicks still
  deselect; shift adds to the existing selection on both clicks
  and marquees. Polygon-vertex lasso stays available when a single
  polygon is the active selection.
- Konva transformer now wraps every selected layer in one shared
  bounding box (polygons fold in for mixed selections; vertex
  handles + the vertex lasso suppress to avoid fighting the box).
  rotateEnabled flips off on multi to skip the ambiguous shared-
  pivot rotation. Drag of any selected node mirrors the delta onto
  every sibling Konva node so the whole group travels together;
  transformend persists each layer's final pose, not just the
  anchor's.
- liveLayerPose became a per-id map (liveLayerPoses) so the
  reactive shape configs don't snap non-focused siblings back to
  their sampled pre-transform pose mid-gesture.
- Plain click on a member of an existing multi-selection no longer
  collapses to single-select before the drag begins.
- Arrow-key nudge + Timeline + keyframe button + Properties panel
  all fan out across the multi-selection: every editable layer
  gets the value, kind-specific panel sections (text, polygon,
  fill, stroke, blur, shadow, mask, button) collapse to leave just
  Transform + Opacity, and the trash button labels with the
  selection count.
- Click on empty stage with a polygon selected now deselects the
  layer too instead of leaving the polygon stuck in the panel.

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

src/i18n/messages.ts

@@ -155,6 +155,8 @@ export const en = {
     interpolated: 'Interpolated',
     removeKeyframe: 'Remove keyframe here',
     deleteLayer: 'Delete layer',
+    deleteLayers: 'Delete {n} layers',
+    multiSelected: '{n} layers selected — edits apply to all',
     noLayer: 'No layer selected.',
     lockedLayer:
       'Selected layer is locked. Unlock the track (or its group) to edit properties.',