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/虫顎/part.yaml

@@ -0,0 +1,88 @@
+id: 虫顎
+original_key: 虫顎
+resource: 肢左
+morph_x: 2
+morph_y: 1
+variants:
+- x: 0
+  y: 0
+  file: x0y0.svg
+- x: 1
+  y: 0
+  file: x1y0.svg
+- x: 1
+  y: 1
+  file: x1y1.svg
+fields:
+- name: 顎
+- name: 節
+- name: 牙
+joints:
+- position: [
+  0.016024151425233186,
+  0.02069910631105899
+]
+- position: [
+  0.01673792698586274,
+  0.02022208689283709
+]
+- position: [
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+  0.018450694378269978
+]
+- position: [
+  0.03221474363901859,
+  0.03379225327609791
+]
+- position: [
+  0.02928913882352495,
+  0.053880697500981733
+]
+- position: [
+  0.03193403153806857,
+  0.061281186848646224
+]
+- position: [
+  0.035539486884306686,
+  0.06744109178239681
+]
+- position: [
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+  0.052023362588319105
+]
+- position: [
+  0.0093312044833953,
+  0.011152769902399133
+]
+- 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: [
+  0.007288961556993493,
+  0.00775832499658671
+]
+- position: [
+  0.022768008876820803,
+  0.04644308609615801
+]
+- position: [
+  0.008737147728355139,
+  0.023890166821240077
+]