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/獣翼UpperArm/part.yaml

@@ -0,0 +1,21 @@
+id: 獣翼UpperArm
+original_key: 獣翼上腕
+resource: 腕左
+morph_x: 1
+morph_y: 1
+variants:
+- x: 0
+  y: 0
+  file: x0y0.svg
+fields:
+- name: 獣翼上腕
+- name: 鱗
+joints:
+- position: [
+  0.058090923706733015,
+  0.06675256824373756
+]
+- position: [
+  0.0772455488959185,
+  0.06739140739968597
+]