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/node_constraint1/property_group.py

@@ -0,0 +1,25 @@
+# SPDX-License-Identifier: MIT OR GPL-3.0-or-later
+from typing import TYPE_CHECKING
+
+from bpy.props import BoolProperty
+from bpy.types import PropertyGroup
+
+
+# https://github.com/vrm-c/vrm-specification/blob/6fb6baaf9b9095a84fb82c8384db36e1afeb3558/specification/VRMC_springBone-1.0-beta/schema/VRMC_springBone.schema.json
+class NodeConstraint1NodeConstraintPropertyGroup(PropertyGroup):
+    # for UI
+    show_expanded_roll_constraints: BoolProperty(  # type: ignore[valid-type]
+        name="Roll Constraint"
+    )
+    show_expanded_aim_constraints: BoolProperty(  # type: ignore[valid-type]
+        name="Aim Constraint"
+    )
+    show_expanded_rotation_constraints: BoolProperty(  # type: ignore[valid-type]
+        name="Rotation Constraint"
+    )
+    if TYPE_CHECKING:
+        # This code is auto generated.
+        # To regenerate, run the `uv run tools/property_typing.py` command.
+        show_expanded_roll_constraints: bool  # type: ignore[no-redef]
+        show_expanded_aim_constraints: bool  # type: ignore[no-redef]
+        show_expanded_rotation_constraints: bool  # type: ignore[no-redef]