feat: Add VRM Blender addon with complete import/export functionality

- Add core VRM addon infrastructure with manifest and registration
- Add common utilities module with file system, logging, and conversion helpers
- Add human bone mapper with support for multiple rigging standards (Mixamo, MMD, Unreal, Rigify, etc.)
- Add VRM 0.x and 1.x format support with property groups and handlers
- Add editor UI panels for VRM metadata, spring bones, and MToon materials
- Add exporter with glTF2 extension support for VRM format serialization
- Add importer with scene reconstruction and armature generation
- Add MToon shader support with auto-setup and material migration
- Add spring bone physics simulation with constraint handling
- Add node constraint editor for advanced rigging control
- Add comprehensive validation and error handling with user dialogs
- Add scene watcher for real-time property synchronization
- Add workspace management and preference system
- Include Python cache files and Blender manifest configuration
- This is the initial commit establishing the complete VRM addon ecosystem for Blender

blender_manifest.toml

@@ -0,0 +1,26 @@
+schema_version = "1.0.0"
+
+id = "vrm"
+version = "3.17.1"
+
+name = "VRM format"
+tagline = "VRM import, export and editing capabilities"
+maintainer = "Isamu Mogi <dyob@lunaport.net>"
+type = "add-on"
+
+website = "https://vrm-addon-for-blender.info"
+
+tags = ["Import-Export", "Animation", "Modeling", "Material", "Physics"]
+
+blender_version_min = "4.2.0"
+blender_version_max = "5.1.0"
+
+license = ["SPDX:MIT", "SPDX:GPL-3.0-or-later"]
+
+copyright = [
+  "2020 Isamu Mogi",
+  "2018 iCyP",
+]
+
+[permissions]
+files = "Import/export VRM from/to disk"