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/四足腿/part.yaml

@@ -0,0 +1,87 @@
+id: 四足腿
+original_key: 四足腿
+resource: 脚左
+morph_x: 4
+morph_y: 1
+variants:
+- x: 0
+  y: 0
+  file: x0y0.svg
+- x: 1
+  y: 0
+  file: x1y0.svg
+- x: 2
+  y: 0
+  file: x2y0.svg
+- x: 3
+  y: 0
+  file: x3y0.svg
+fields:
+- name: 腿
+- name: 筋
+- name: 虎左
+joints:
+- position: [
+  0.11194263600754599,
+  0.10571460191115639
+]
+- position: [
+  0.1117083140790576,
+  0.07214836701320834
+]
+- position: [
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+]
+- position: [
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+  0.07342168211652943
+]
+- position: [
+  0.11031709800272728,
+  0.10134361752011758
+]
+- position: [
+  0.11143014087301314,
+  0.0710235536002995
+]
+- position: [
+  0.11355107243694557,
+  0.10465523790410822
+]
+- position: [
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+  0.07226528141655214
+]
+- position: [
+  0.0490874502418095,
+  0.048757335555755205
+]
+- position: [
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+  0.028674150923734126
+]
+- position: [
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+]
+- position: [
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+]
+- position: [
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+]
+- position: [
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+  0.05552075312068708
+]
+- position: [
+  0.029010185017340477,
+  0.0052625889657564665
+]
+- position: [
+  0.029600224187073074,
+  0.003343390263891001
+]