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/鳥翼UpperArm/part.yaml

@@ -0,0 +1,36 @@
+id: 鳥翼UpperArm
+original_key: 鳥翼上腕
+resource: 腕左
+morph_x: 1
+morph_y: 1
+variants:
+- x: 0
+  y: 0
+  file: x0y0.svg
+fields:
+- name: 風切羽
+- name: 羽毛
+- name: 鳥翼上腕
+- name: 小雨覆
+- name: 鱗
+joints:
+- position: [
+  0.05794209672584697,
+  0.07029176926338121
+]
+- position: [
+  0.06965245143667854,
+  0.07580889040767418
+]
+- position: [
+  0.07787353124941195,
+  0.074099274959161
+]
+- position: [
+  0.08689726611611695,
+  0.0718504591334438
+]
+- position: [
+  0.06996703136331828,
+  0.06988906241785904
+]