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/四足胴/part.yaml

@@ -0,0 +1,38 @@
+id: 四足胴
+original_key: 四足胴
+resource: 半身
+morph_x: 1
+morph_y: 1
+variants:
+- x: 0
+  y: 0
+  file: x0y0.svg
+fields:
+- name: 胴
+- name: 筋肉
+- name: 獣性
+joints:
+- position: [
+  0.4873770033272495,
+  0.5357691950513394
+]
+- position: [
+  0.5126229966727514,
+  0.5357691950513394
+]
+- position: [
+  0.47495676774447676,
+  0.539655119777143
+]
+- position: [
+  0.5250432322555232,
+  0.539655119777143
+]
+- position: [
+  0.5,
+  0.5418849046619865
+]
+- position: [
+  0.5000000000000004,
+  0.5357691950513394
+]