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/四足留具前/part.yaml

@@ -0,0 +1,53 @@
+id: 四足留具前
+original_key: 四足留具前
+resource: 半身
+morph_x: 1
+morph_y: 1
+variants:
+- x: 0
+  y: 0
+  file: x0y0.svg
+fields:
+- name: 革1
+- name: 革2
+- name: 丸金具1
+- name: 丸金具2
+- name: 革3
+- name: 丸金具3
+- name: 丸金具左1
+- name: 丸金具右1
+- name: 丸金具左2
+- name: 丸金具右2
+joints:
+- position: [
+  0.018432339988539145,
+  0.00455474685707178
+]
+- position: [
+  0.018432339988539145,
+  0.025546725680459566
+]
+- position: [
+  0.018432339988539145,
+  0.012032899610196044
+]
+- position: [
+  0.012394379976631396,
+  0.014128894294483885
+]
+- position: [
+  0.005272122775181902,
+  -0.0001944609581425543
+]
+- position: [
+  0.019516637178080894,
+  -0.0001944609581425543
+]
+- position: [
+  0.007080699538770417,
+  0.019208733193176168
+]
+- position: [
+  0.017708152439562697,
+  0.019208733193176168
+]