figma-transformer: decode stroke weight/align/dashes so borders render at design width

[chubes4]

Summary

Per coverage issue #328, the Kiwi decoder's NodeChange field policy never whitelisted the stroke geometry fields, so strokeWeight/strokeAlign/dashPattern were dropped during selective decode. The emitter's strokeStyles() already read strokeWeight/strokeAlign, but with those fields gone every border rendered at the 1px default regardless of the design.

Changes

• FigKiwiDecoder — whitelist strokeWeight, strokeAlign, strokeCap, strokeJoin, dashPattern, and the per-side border weights on the NodeChange policy. Per-side names are over-listed across both border*Weight/stroke*Weight shapes; unlisted fields are skipped (not mis-read), so the over-list is safe.

• ScenegraphNormalizer — carry the stroke fields through component-instance resolution and instance-child override merges so instances render their own strokes.

• StaticHtmlEmitter::strokeStyles() — honour the decoded geometry:

  • real strokeWeight on the border / outside box-shadow ring
  • per-side border-*-width when independent weights are present
  • box-sizing:border-box for INSIDE strokes so the box isn't grown
  • border-style:dashed for a non-empty dashPattern

  CSS borders can't reproduce exact Figma dash lengths (border-style only exposes the dashed keyword); precise dashes would need an SVG/background stroke, which is out of scope here.

Test

php tests/contract/run.php — all pass. New coverage:

• A real Kiwi decode fixture (schema + message through the generic decoder) proving strokeWeight=3, strokeAlign=INSIDE and dashPattern=[4,2] survive the field policy.
• An emitter fixture asserting an INSIDE stroke emits the exact border:3px solid #000000;box-sizing:border-box (no longer the 1px default).
• An emitter fixture asserting a dashPattern emits border-style:dashed at the design width.

Refs #328

AI assistance

• AI assistance: Yes
• Tool(s): Claude Sonnet 4.6 via Claude Code
• Used for: Implementation