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/四足留具後/part.yaml

@@ -0,0 +1,47 @@
+id: 四足留具後
+original_key: 四足留具後
+resource: 半身
+morph_x: 1
+morph_y: 1
+variants:
+- x: 0
+  y: 0
+  file: x0y0.svg
+fields:
+- name: 革左
+- name: 革右
+- name: 丸金具1
+- name: 革
+- name: 丸金具2
+- name: 丸金具3
+- name: 丸金具4
+- name: 丸金具5
+joints:
+- position: [
+  0.0077602513316739384,
+  -0.006534560961206891
+]
+- position: [
+  0.011108154742667742,
+  0.008501135162713513
+]
+- position: [
+  0.014545739131303415,
+  -0.0032519956032064064
+]
+- position: [
+  0.011158992400397201,
+  0.012017310085419742
+]
+- position: [
+  0.011196562844302895,
+  0.0025096983322777638
+]
+- position: [
+  0.007396567942713693,
+  0.016910281288054302
+]
+- position: [
+  0.014908971862084558,
+  0.016910281288054302
+]