feat(body_mesh): Add body mesh separator module with edge dissolution

- Add body_mesh submodule with VRM_OT_separate_non_skin_faces operator
- Add VRM_PT_body_mesh_separator panel for UI integration
- Add utility functions for mesh operations and edge dissolution logic
- Add comprehensive edge dissolution configuration files for all body parts (head, torso, arms, legs, hands) with UV coordinates
- Add test utilities for validating mesh separation operations
- Add .gitignore to exclude Python cache files and test artifacts
- Register body_mesh module in editor package initialization
- Update registration.py to include new body mesh components

registration.py

@@ -43,6 +43,8 @@ from .editor import (
     subscription,
     validation,
 )
+from .editor.body_mesh import ops as body_mesh_ops
+from .editor.body_mesh import panel as body_mesh_panel
 from .editor.mtoon1 import handler as mtoon1_handler
 from .editor.mtoon1 import ops as mtoon1_ops
 from .editor.mtoon1 import panel as mtoon1_panel
@@ -267,6 +269,7 @@ classes: list[
     panel.VRM_PT_controller_unsupported_blender_version_warning,
     panel.VRM_PT_controller,
     panel.VRM_PT_vrm_armature_object_property,
+    body_mesh_panel.VRM_PT_body_mesh_separator,
     vrm0_menu.VRM_MT_vrm0_blend_shape_master,
     vrm0_ui_list.VRM_UL_vrm0_first_person_mesh_annotation,
     vrm0_ui_list.VRM_UL_vrm0_blend_shape_bind,
@@ -430,6 +433,7 @@ classes: list[
     ops.VRM_OT_show_blend_file_compatibility_warning,
     ops.VRM_OT_show_blend_file_addon_compatibility_warning,
     ops.VRM_OT_make_estimated_humanoid_t_pose,
+    body_mesh_ops.VRM_OT_separate_non_skin_faces,
     validation.VrmValidationError,
     validation.WM_OT_vrm_validator,
     export_scene.WM_OT_vrm_export_human_bones_assignment,