feat(miku): proper rigged model from Sketchfab + Blender

Pipeline:
1. Downloaded TDA-style Miku model from Sketchfab (19MB FBX, 38K verts)
2. Imported to Blender, scaled to Godot humanoid proportions (1.8u tall)
3. Created clean 17-bone humanoid armature (Hips/Spine/Chest/Head/Arms/Legs)
4. Auto-weight-painted mesh to armature
5. Added Idle (breath bounce) and Run (cycle) animations
6. Exported as GLB with embedded animations (3MB)

New:
- SkinnedPlayerModel class: loads GLB with own armature+animations
- Player 1 spawns with Miku model, others get procedural humanoid
- Completely separate from procedural model system

Files:
- assets/characters/skins/miku_rigged_final.glb (3MB, 48K verts, 17 bones, 2 anims)
- characters/skinned_player_model.gd
- Removed old procedural GLB attempts

characters/skinned_player_model.gd

@@ -0,0 +1,88 @@
+extends Node3D
+class_name SkinnedPlayerModel
+
+## A player model loaded from a GLB file with its own armature and animations.
+## Replaces the procedural HumanoidModel for characters with custom skins.
+
+@export var model_path: String = ""
+
+var skeleton: Skeleton3D
+var animation_player: AnimationPlayer
+var animation_tree: AnimationTree
+
+func _ready() -> void:
+	if model_path != "":
+		load_model(model_path)
+
+func load_model(path: String) -> void:
+	# Clear existing children
+	for child in get_children():
+		child.queue_free()
+	
+	var loaded = load(path)
+	if not loaded:
+		print("SkinnedPlayerModel: failed to load %s" % path)
+		return
+	
+	var scene = loaded.instantiate()
+	if not scene:
+		print("SkinnedPlayerModel: failed to instantiate %s" % path)
+		return
+	
+	add_child(scene)
+	
+	# Find skeleton and animation player
+	skeleton = find_skeleton(scene)
+	animation_player = find_animation_player(scene)
+	
+	if animation_player:
+		print("SkinnedPlayerModel: loaded '%s' with %d animations" % [
+			path, animation_player.get_animation_list().size()
+		])
+		for anim in animation_player.get_animation_list():
+			print("  - %s" % anim)
+	else:
+		print("SkinnedPlayerModel: no animation player found")
+
+func find_skeleton(node: Node) -> Skeleton3D:
+	if node is Skeleton3D:
+		return node
+	for child in node.get_children():
+		var result = find_skeleton(child)
+		if result:
+			return result
+	return null
+
+func find_animation_player(node: Node) -> AnimationPlayer:
+	if node is AnimationPlayer:
+		return node
+	for child in node.get_children():
+		var result = find_animation_player(child)
+		if result:
+			return result
+	return null
+
+func play_animation(name: String) -> void:
+	if animation_player and animation_player.has_animation(name):
+		animation_player.play(name)
+	else:
+		print("SkinnedPlayerModel: animation '%s' not found" % name)
+
+func update_state(state: String, speed: float, is_crouching: bool = false) -> void:
+	if not animation_player:
+		return
+	
+	match state:
+		"ground", "idle":
+			if speed > 1.0:
+				play_animation("Run")
+			else:
+				play_animation("Idle")
+		"air":
+			play_animation("Idle")  # TODO: add jump/fall anim
+		"crouch":
+			play_animation("Idle")  # TODO: add crouch anim
+		"slide":
+			play_animation("Run")  # TODO: add slide anim
+		_:
+			play_animation("Idle")