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/lib/interpolate.ts

@@ -62,6 +62,12 @@ function lerpProps(a: AnimatableProps, b: AnimatableProps, t: number): Animatabl
   if (a.shadowColor && b.shadowColor) out.shadowColor = lerpColor(a.shadowColor, b.shadowColor, t)
   else if (b.shadowColor) out.shadowColor = b.shadowColor
   else if (a.shadowColor) out.shadowColor = a.shadowColor
+  if (a.stroke && b.stroke) out.stroke = lerpColor(a.stroke, b.stroke, t)
+  else if (b.stroke) out.stroke = b.stroke
+  else if (a.stroke) out.stroke = a.stroke
+  if (a.strokeWidth !== undefined && b.strokeWidth !== undefined) out.strokeWidth = lerp(a.strokeWidth, b.strokeWidth, t)
+  else if (b.strokeWidth !== undefined) out.strokeWidth = b.strokeWidth
+  else if (a.strokeWidth !== undefined) out.strokeWidth = a.strokeWidth
   if (a.points && b.points && a.points.length === b.points.length) {
     out.points = a.points.map((pa, i) => {
       const pb = b.points![i]