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/頬肌左/part.yaml

@@ -0,0 +1,59 @@
+id: 頬肌左
+original_key: 頬肌左
+resource: 胴体
+morph_x: 1
+morph_y: 1
+variants:
+- x: 0
+  y: 0
+  file: x0y0.svg
+fields:
+- name: 淫タトゥ
+- name: 悪タトゥ
+- name: 隈取
+- name: 猟豹
+- name: 牛柄
+- name: 獣性
+- name: 紋柄
+- name: 鱗
+- name: 百足
+- name: 蜘蛛
+- name: 傷
+- name: 髭
+joints:
+- position: [
+  -0.0014957944219115837,
+  0.008105469171541388
+]
+- position: [
+  0.05035769541395883,
+  0.04346315328116932
+]
+- position: [
+  0.05038074040652705,
+  0.04412307552525584
+]
+- position: [
+  0.051715138554187,
+  0.047070880101016226
+]
+- position: [
+  0.05173818354675522,
+  0.04773080234510274
+]
+- position: [
+  0.0545986291310103,
+  0.04426074024106696
+]
+- position: [
+  0.05462167412357852,
+  0.04492066248515347
+]
+- position: [
+  0.05048673132780686,
+  0.04407256151519765
+]
+- position: [
+  0.05048673132780685,
+  0.04473288601112572
+]