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/獣耳/part.yaml

@@ -0,0 +1,53 @@
+id: 獣耳
+original_key: 獣耳
+resource: 肢左
+morph_x: 2
+morph_y: 3
+variants:
+- x: 0
+  y: 0
+  file: x0y0.svg
+- x: 0
+  y: 1
+  file: x0y1.svg
+- x: 0
+  y: 2
+  file: x0y2.svg
+- x: 1
+  y: 0
+  file: x1y0.svg
+- x: 1
+  y: 1
+  file: x1y1.svg
+- x: 1
+  y: 2
+  file: x1y2.svg
+fields:
+- name: 獣耳外
+- name: 獣耳内
+- name: 耳毛
+joints:
+- position: [
+  0.047807303068763296,
+  0.05738719212623395
+]
+- position: [
+  0.060046257626335475,
+  0.05708285869382676
+]
+- position: [
+  0.048378587284308466,
+  0.05603120784293215
+]
+- position: [
+  0.059296414099024794,
+  0.05942676781153709
+]
+- position: [
+  0.04909757762377233,
+  0.05513843230448154
+]
+- position: [
+  0.05823156619435935,
+  0.06102102321619785
+]