Add stroke align, individual side strokes, and side selector UI
- Renderer: stroke align (INSIDE/CENTER/OUTSIDE) using clip-based
approach for all shape types including sections
- Renderer: individual side strokes when independentStrokeWeights is
enabled, drawing per-side lines with correct align offsets
- StrokeSection: align dropdown, side selector dropdown (All/Top/Bottom/
Left/Right/Custom), individual weight inputs with side-specific icons
- Kiwi serialize: export correct strokeAlign and border weight fields
- Scene graph: sync border weight props through instance sync
- 19 tests covering align, individual weights, instance sync, kiwi
export, and FigmaAPI properties
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