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/Shoulder/part.yaml

@@ -0,0 +1,33 @@
+id: Shoulder
+original_key: 肩
+resource: 肩左
+morph_x: 1
+morph_y: 1
+variants:
+- x: 0
+  y: 0
+  file: x0y0.svg
+fields:
+- name: 脇
+- name: 肩
+joints:
+- position: [
+  0.030850908155102816,
+  0.06745715429702073
+]
+- position: [
+  0.03969795971544586,
+  0.07221140108871305
+]
+- position: [
+  0.0562503924684768,
+  0.06022872118377538
+]
+- position: [
+  0.03825814978767629,
+  0.06551608770860626
+]
+- position: [
+  0.03016810701801849,
+  0.06728509033885754
+]