0.3.0: freeform drawing, stroke properties, polygon edit gestures

- Freeform drawing tool: new sidebar button enters a click-to-draw mode
  that appends points, shows a live ghost preview line, and exits via
  Enter or double-click (near the start point closes the path). Works
  end-to-end through all four render pipelines.
- Polygon authoring gestures: double-click on a path inserts a vertex on
  the nearest edge; double-click on an open polygon's endpoint resumes
  the drawing session from that end, reversing point order when needed.
- Stroke + closed-path properties: all shape types (rect, circle, text,
  polygon) expose stroke color, stroke width, and (for polygons) a
  closed toggle. Fill and stroke each support a "transparent" switch so
  shapes can render as outline-only or fill-only.
- Mask preview no longer inherits the user's stroke — the dashed ghost
  keeps its own outline regardless of stroke-width changes.
- Playhead no longer dims on inactive timeline tracks; only keyframes,
  segments and clip blocks fade.
- Properties panel point-count control for polygons, plus per-keyframe
  points animation that correctly interpolates once a baseline exists.
- Pivot drag hides the rotation handle until release.
- Transformer attach retries on a short timer to avoid races where the
  Konva node hasn't mounted yet when selection changes.

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

src/i18n/messages.ts

@@ -65,6 +65,8 @@ export const en = {
       circle: 'Circle',
       text: 'Text',
       polygon: 'Polygon',
+      freeform: 'Freeform (click to draw, Enter to finish, Esc to cancel)',
+      freeformActive: 'Drawing… (Enter to finish, Esc to cancel)',
     },
     newTextDialog: {
       title: 'New text object',
@@ -73,6 +75,11 @@ export const en = {
       confirm: 'Insert',
       fallback: 'Text',
     },
+    newPolygonDialog: {
+      title: 'New polygon',
+      message: 'Number of points (3–24):',
+      confirm: 'Create',
+    },
     newClipDialog: {
       title: 'New clip',
       message: 'Clip name:',
@@ -97,13 +104,20 @@ export const en = {
     deleteLayer: 'Delete layer',
     noLayer: 'No layer selected.',
     fill: 'Fill',
+    transparent: 'Transparent',
     opacity: 'Opacity',
     edgeBlur: 'Edge blur',
     sections: {
       transform: 'Transform',
       text: 'Text',
+      polygon: 'Polygon',
       appearance: 'Appearance',
     },
+    polygonPoints: 'Points',
+    polygonPointsHint: 'Changing the point count rewrites all keyframes; new points are inserted at the midpoint of the last edge.',
+    polygonClosed: 'Closed path (fill)',
+    stroke: 'Stroke',
+    strokeWidth: 'Stroke width',
     shadow: 'Shadow',
     shadowBlur: 'Shadow blur',
     shadowOpacity: 'Shadow opacity',