feat(vrm_mesh_tools): Add standalone VRM mesh tools addon with separation and UV merging

- Add VRM Mesh Tools addon as independent Blender extension with complete functionality
- Implement Body Mesh Separator operator to isolate non-skin materials (CLOTH, etc.) from Body mesh
- Implement UV Edge Merger operator to convert triangles to quads based on UV coordinates
- Add comprehensive UI panel in sidebar with material list and operation buttons
- Include UV edge data JSON files for 10 VRM material types (Body, Face, Eyes, Hair, etc.)
- Add detailed README with installation instructions, usage guide, and compatibility notes
- Configure addon manifest for Blender 4.2+ with proper namespace isolation (vrm_mesh_tools)
- Ensure full compatibility with official VRM addon through independent naming conventions
- Add utility functions for mesh operations, material detection, and JSON data loading

vrm_mesh_tools/blender_manifest.toml

@@ -0,0 +1,19 @@
+schema_version = "1.0.0"
+
+id = "vrm_mesh_tools"
+version = "1.0.0"
+
+name = "VRM Mesh Tools"
+tagline = "Standalone mesh separation and UV edge merging tools for VRM models"
+maintainer = "VRM Mesh Tools Contributors"
+type = "add-on"
+
+tags = ["Modeling", "Mesh"]
+
+blender_version_min = "4.2.0"
+
+license = ["SPDX:MIT"]
+
+copyright = [
+  "2026 VRM Mesh Tools Contributors",
+]