feat: add rigged+animated Miku player model with auto-rig pipeline

- Add miku_rigged_animated.glb (3.27MB) with 18-bone skeleton and 6 animations
  (Idle, Walk, Run, Jump, Crouch, Death) via Blender auto-rig script
- Add tools/rig_and_animate.py: reusable Blender script for rigging any humanoid
  mesh with Mixamo-compatible bone naming
- Update SkinnedPlayerModel: scale_factor, first-person mode, animation state
  matching (Idle/Walk/Run/Jump/Crouch/Death)
- Update level_runtime.gd: use skinned model for local player, procedural
  humanoid for remote players
- Update skin_manager.gd and test_level_builder.gd to use animated model
- Fix Godot 4.2.1 'is not Type' syntax in 5 weapon files
- Add editor/import_miku_to_tscn.gd for editor-based GLB import

editor/import_miku_to_tscn.gd

@@ -0,0 +1,37 @@
+@tool
+extends EditorScript
+
+func _run():
+    var source = "res://assets/characters/skins/miku_rigged_final.glb"
+    var dest = "res://assets/characters/skins/miku_rigged.tscn"
+    
+    print("Loading %s..." % source)
+    var glb = load(source)
+    if not glb:
+        print("ERROR: Failed to load GLB")
+        return
+    
+    print("Instantiating...")
+    var scene = glb.instantiate()
+    if not scene:
+        print("ERROR: Failed to instantiate")
+        return
+    
+    print("Scene: %s" % scene.name)
+    print("Children:")
+    for child in scene.get_children():
+        print("  %s (%s)" % [child.name, child.get_class()])
+        if child is Skeleton3D:
+            print("    Bones: %d" % child.get_bone_count())
+            for i in range(child.get_bone_count()):
+                var bone_name = child.get_bone_name(i)
+                var rest = child.get_bone_global_rest(i)
+                print("      %s: pos=%s" % [bone_name, rest.origin])
+        if child is AnimationPlayer:
+            print("    Animations: %s" % child.get_animation_list())
+    
+    # Save as scene
+    var packed = PackedScene.new()
+    packed.pack(scene)
+    ResourceSaver.save(packed, dest)
+    print("Saved to %s" % dest)