fix: create proper Idle animation in Godot when GLB export loses tracks

The Blender GLTF exporter was stripping animation tracks (only 1 of 51
channels survived export). Now SkinnedPlayerModel detects this at
runtime and creates a proper Idle animation programmatically using Godot's
Animation API with 5 bone tracks (Spine, Arms, Neck, Hips).

Also switched model_path back to miku_rigged_final.glb since the
re-export wasn't adding usable animations.

scenes/maps/level_runtime.gd

@@ -147,7 +147,7 @@ func _spawn_player(pid: int) -> CharacterBody3D:
 		# Local player: use skinned Miku model with animations
 		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.model_path = "res://assets/characters/skins/miku_rigged_final.glb"
 		skinned.position = Vector3(0, 0.0, 0)
 		skinned.first_person_mode = true
 		player.add_child(skinned)