* build(core): import Markdown with unplugin-raw
Core inlined ?raw imports with a hand-written Rolldown plugin that also turned plain .md imports into strings, which nothing in Core uses. unplugin-raw already does this for the Vue SDK and design-jsx; use it here too and drop the unused *.md module declaration.
* refactor(pen): use the scene-graph color parser
pen/src/color.ts duplicated parseColor from @open-pencil/scene-graph/color line for line. Import it instead, which also drops pen's direct culori dependency.
* fix(figma-api): validate effects like Figma
The effects setter stored whatever a script passed, so scripts that Figma rejects ran here and malformed effects reached rendering and .fig export. Validate against Figma's effect shapes with Valibot, recorded from live Figma: strict objects, required shadow fields, radius >= 0, RGBA channels within 0..1, and no shadow fields on blurs. The getter now returns Figma's shape so node.effects = node.effects keeps working.
Closes#786
* fix(figma-api): reject infinite numbers in effects
Figma rejects Infinity in every effect number ("Number must be finite"), but v.number() accepts it, so infinite radii, offsets, and spreads reached the scene graph.
* fix(figma-api): store PASS_THROUGH shadow blend as NORMAL
PASS_THROUGH is a layer blend mode. Live Figma accepts it on drop and inner shadows but reads NORMAL back, so do the same instead of storing it.
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