feat: add 3D model viewer, HUD panel updates, and eskin-finger-sdk submodule

- Add ModelStage component for 3D model rendering
- Update CenterStage to integrate ModelStage viewer
- Expand HudPanel with new functionality
- Add HUD type definitions
- Add je-skin-model.glb 3D model asset
- Add eskin-finger-sdk as git submodule

static/models/README.md

@@ -0,0 +1,14 @@
+# 3D model assets
+
+Put the first pipeline model here:
+
+- Preferred: `static/models/je-skin-model.glb`
+- Format: glTF 2.0 `.glb`
+- Also supported after changing `modelUrl`: glTF 2.0 `.gltf` with its `.bin` and texture files in the same folder
+- Not supported directly: older glTF 1.0 assets. Convert them to glTF 2.0 first.
+
+Runtime URL used by the app:
+
+```text
+/models/je-skin-model.glb
+```