Phase 0.3-0.5: SVG export + YAML sidecars + asset catalog

- Add hair class KeyMap entries (基髪→BaseHair, 前髪→FrontHair, 胸毛→ChestHair)
- Implement cardinal spline → cubic Bezier SVG export for all 175 body parts
- Generate YAML sidecar files (part.yaml) per part with metadata
- Write Catalog.yaml index for runtime asset loading
- Output to SlaveMatrix/Assets/Parts/{EnglishName}/ structure
- Each part directory contains part.yaml + x{x}y{y}.svg morph variants
- 838 SVGs across 324 morph variants, 175 sidecars, 1 catalog
- Extraction tool now serves as the asset build pipeline step

SlaveMatrix/Assets/Parts/四足LowerArm/part.yaml

@@ -0,0 +1,98 @@
+id: 四足LowerArm
+original_key: 四足下腕
+resource: 腕左
+morph_x: 2
+morph_y: 1
+variants:
+- x: 0
+  y: 0
+  file: x0y0.svg
+- x: 1
+  y: 0
+  file: x1y0.svg
+fields:
+- name: 下腕
+- name: 筋肉
+- name: 鱗
+- name: 腕輪
+joints:
+- position: [
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+]
+- position: [
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+- position: [
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+- position: [
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+- position: [
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+- position: [
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