fix: correct skin deformation and scale for GLB character models

The Miku model T-posed because the previous _update_skin() used
set_bone_pose(i, get_bone_pose(i)) which is a no-op when the pose
is unchanged. Replace with skeleton.notification(NOTIFICATION_UPDATE_SKELETON)
to force the Skeleton3D to recompute bone transforms and notify the
MeshInstance to update vertex buffers.

Also fix scale: the GLB is ~1.2m tall (not 1.6m as documented), so
set scale_factor=1.25 to fit the 1.8m player capsule, and add
position_y_offset=-0.2 to align the model's feet with the player origin.

Co-Authored-By: Hermes Agent <[email protected]>

debug/test_level_builder.gd

@@ -433,7 +433,8 @@ func _spawn_player(pid: int) -> CharacterBody3D:
 		var skinned = load("res://characters/skinned_player_model.gd").new()
 		skinned.name = "SkinnedModel"
 		skinned.model_path = "res://assets/characters/skins/miku_rigged_animated.glb"
-		skinned.scale_factor = 1.0  # Already scaled to 1.8m in Blender
+		skinned.scale_factor = 1.25  # GLB is ~1.2m, scale to ~1.5m for player capsule
+		skinned.position_y_offset = -0.2  # Align feet with player origin
 		skinned.position = Vector3.ZERO  # Model origin = player origin
 		player.add_child(skinned)
 		print("TestLevelBuilder: added SkinnedModel for player 1")