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/vrm1/menu.py

@@ -0,0 +1,26 @@
+# SPDX-License-Identifier: MIT OR GPL-3.0-or-later
+from bpy.types import Context, Menu
+
+from ...common.logger import get_logger
+from ..ops import layout_operator
+from ..search import current_armature
+from .ops import VRM_OT_restore_vrm1_expression_morph_target_bind_object
+
+logger = get_logger(__name__)
+
+
+class VRM_MT_vrm1_expression(Menu):
+    bl_label = "Expression Menu"
+    bl_idname = "VRM_MT_vrm1_expression"
+
+    def draw(self, context: Context) -> None:
+        layout = self.layout
+
+        armature = current_armature(context)
+        if not armature:
+            return
+
+        op = layout_operator(
+            layout, VRM_OT_restore_vrm1_expression_morph_target_bind_object
+        )
+        op.armature_object_name = armature.name