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UpperArm/part.yaml

@@ -0,0 +1,51 @@
+id: 四足UpperArm
+original_key: 四足上腕
+resource: 腕左
+morph_x: 2
+morph_y: 1
+variants:
+- x: 0
+  y: 0
+  file: x0y0.svg
+- x: 1
+  y: 0
+  file: x1y0.svg
+fields:
+- name: 筋肉上
+- name: 上腕
+- name: 筋肉下
+- name: 虎柄
+- name: 鱗
+joints:
+- position: [
+  0.0776090258406749,
+  0.0666146658662219
+]
+- position: [
+  0.05636515080019466,
+  0.06626143700652762
+]
+- position: [
+  0.009307784641308431,
+  -0.023539039544349737
+]
+- position: [
+  0.008842682619453885,
+  -0.02328738079580974
+]
+- position: [
+  0.008073215725038512,
+  -0.022975682007035987
+]
+- position: [
+  0.03829360131887328,
+  0.0050548530859284855
+]
+- position: [
+  0.09118582473193013,
+  0.07089467187295634
+]
+- position: [
+  0.08706011231230343,
+  0.06548408928052393
+]