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LowerArm/part.yaml

@@ -0,0 +1,54 @@
+id: 獣翼LowerArm
+original_key: 獣翼下腕
+resource: 腕左
+morph_x: 1
+morph_y: 1
+variants:
+- x: 0
+  y: 0
+  file: x0y0.svg
+fields:
+- name: 獣翼下腕
+- name: 鱗
+- name: 腕輪
+joints:
+- position: [
+  0.03412068913527216,
+  0.07620103578939638
+]
+- position: [
+  0.0810114518043974,
+  0.0784192748434503
+]
+- position: [
+  0.06320524067494648,
+  0.08551910816375946
+]
+- position: [
+  0.011152769902399136,
+  0.014743453741191456
+]
+- position: [
+  0.011152769902399133,
+  0.0034740277007159455
+]
+- position: [
+  0.011152769902399136,
+  0.023700590279325286
+]
+- position: [
+  0.011152769902399133,
+  -0.0013950504745270235
+]
+- position: [
+  0.007758324996586714,
+  0.011941093891509465
+]
+- position: [
+  0.009906215631991292,
+  0.010736178205088369
+]
+- position: [
+  0.005610434361182023,
+  0.004780471788085029
+]