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

editor/vrm0/handler.py

@@ -0,0 +1,37 @@
+# SPDX-License-Identifier: MIT OR GPL-3.0-or-later
+import bpy
+from bpy.app.handlers import persistent
+
+from ...common.logger import get_logger
+from .property_group import Vrm0BlendShapeGroupPropertyGroup
+
+logger = get_logger(__name__)
+
+
+@persistent
+def frame_change_pre(_unused: object) -> None:
+    Vrm0BlendShapeGroupPropertyGroup.frame_change_post_shape_key_updates.clear()
+
+
+@persistent
+def frame_change_post(_unused: object) -> None:
+    context = bpy.context
+
+    for (
+        (
+            shape_key_name,
+            key_block_name,
+        ),
+        value,
+    ) in Vrm0BlendShapeGroupPropertyGroup.frame_change_post_shape_key_updates.items():
+        shape_key = context.blend_data.shape_keys.get(shape_key_name)
+        if not shape_key:
+            continue
+        key_blocks = shape_key.key_blocks
+        if not key_blocks:
+            continue
+        key_block = key_blocks.get(key_block_name)
+        if not key_block:
+            continue
+        key_block.value = value
+    Vrm0BlendShapeGroupPropertyGroup.frame_change_post_shape_key_updates.clear()