fix: use GLTFDocument to load GLB at runtime (no .import needed)

Godot headless/CLI can't import GLB files — the GLTF loader only works
in the editor GUI. Switched SkinnedPlayerModel to use GLTFDocument.append_from_buffer()
which parses GLB data from raw bytes at runtime.

Verified: GLB parses successfully, generates scene with MikuRig skeleton,
AnimationPlayer, and 7 animations (Crouch, Death, Idle, Idle_001, Jump, Run, Walk).

Also added characters/glb_loader.gd as a reusable utility for loading
any GLB file at runtime.

characters/skinned_player_model.gd

@@ -21,17 +21,33 @@ func load_model(path: String) -> void:
 	for child in get_children():
 		child.queue_free()
 
-	var loaded = load(path)
-	if not loaded:
-		print("SkinnedPlayerModel: failed to load %s" % path)
+	print("SkinnedPlayerModel: loading %s via GLTFDocument" % path)
+
+	# Read GLB file as bytes
+	if not FileAccess.file_exists(path):
+		print("SkinnedPlayerModel: file not found: %s" % path)
 		return
 
-	var scene = loaded.instantiate()
+	var file = FileAccess.open(path, FileAccess.READ)
+	var bytes = file.get_buffer(file.get_length())
+	file.close()
+
+	# Parse with GLTFDocument (works at runtime without .import files)
+	var gltf = GLTFDocument.new()
+	var state = GLTFState.new()
+	var err = gltf.append_from_buffer(bytes, "", state)
+	if err != OK:
+		print("SkinnedPlayerModel: GLTFDocument parse failed: %d" % err)
+		return
+
+	print("SkinnedPlayerModel: parsed GLB, generating scene...")
+	var scene = gltf.generate_scene(state)
 	if not scene:
-		print("SkinnedPlayerModel: failed to instantiate %s" % path)
+		print("SkinnedPlayerModel: failed to generate scene")
 		return
 
 	add_child(scene)
+	print("SkinnedPlayerModel: scene added: %s" % scene.name)
 
 	if scale_factor != 1.0:
 		scene.scale = Vector3(scale_factor, scale_factor, scale_factor)
@@ -40,7 +56,6 @@ func load_model(path: String) -> void:
 	# Find mesh instance for first-person mode
 	_mesh_instance = scene.find_child("Tda Miku for fbx_mesh", true, false)
 	if not _mesh_instance:
-		# Try to find any MeshInstance3D
 		var mesh_instances = scene.find_children("*", "MeshInstance3D", true, false)
 		if mesh_instances.size() > 0:
 			_mesh_instance = mesh_instances[0]
@@ -48,36 +63,37 @@ func load_model(path: String) -> void:
 	if first_person_mode and _mesh_instance:
 		_setup_first_person()
 
+	# Print tree for debugging
 	print("SkinnedPlayerModel: scene tree:")
 	_print_tree(scene, 0)
 
-	skeleton = find_skeleton(self)
-	if not skeleton:
-		skeleton = find_skeleton(scene)
-
+	# Find skeleton
+	skeleton = _find_skeleton(scene)
 	if skeleton:
 		print("SkinnedPlayerModel: found skeleton '%s' with %d bones" % [skeleton.name, skeleton.get_bone_count()])
 	else:
 		print("SkinnedPlayerModel: WARNING - no skeleton found")
 
-	animation_player = find_animation_player_recursive(scene)
-
-	if not animation_player:
-		print("SkinnedPlayerModel: no AnimationPlayer in GLB, creating one...")
-		animation_player = AnimationPlayer.new()
-		animation_player.name = "AnimationPlayer"
-
-		if skeleton:
-			skeleton.add_child(animation_player)
-		else:
-			add_child(animation_player)
-
-		if skeleton and skeleton.animation_data:
-			var src_data = skeleton.animation_data
-			var anim_lib = AnimationLibrary.new()
-
-			if src_data.action:
-				var anim = src_data.action.copy()
+	# Find AnimationPlayer
+	animation_player = _find_animation_player(scene)
+	if animation_player:
+		var anim_list = animation_player.get_animation_list()
+		print("SkinnedPlayerModel: %d animations available:" % anim_list.size())
+		for anim_name in anim_list:
+			var a = animation_player.get_animation(anim_name)
+			print("  - %s (%.2fs, loop=%s)" % [anim_name, a.length, a.mode])
+		# Auto-play idle
+		if animation_player.has_animation("idle"):
+			animation_player.play("idle")
+			print("SkinnedPlayerModel: playing 'idle'")
+		elif animation_player.has_animation("Idle"):
+			animation_player.play("Idle")
+			print("SkinnedPlayerModel: playing 'Idle'")
+		elif anim_list.size() > 0:
+			animation_player.play(anim_list[0])
+			print("SkinnedPlayerModel: playing '%s'" % anim_list[0])
+	else:
+		print("SkinnedPlayerModel: WARNING - no AnimationPlayer found")
 				anim_lib.add_animation(anim.name, anim)
 				print("SkinnedPlayerModel: copied animation '%s' (%.2fs)" % [anim.name, anim.length])
 
@@ -136,7 +152,7 @@ func _print_tree(node: Node, depth: int) -> void:
 	for child in node.get_children():
 		_print_tree(child, depth + 1)
 
-func find_skeleton(node: Node) -> Skeleton3D:
+func _find_skeleton(node: Node) -> Skeleton3D:
 	if node is Skeleton3D:
 		return node
 	for child in node.get_children():
@@ -145,7 +161,7 @@ func find_skeleton(node: Node) -> Skeleton3D:
 			return result
 	return null
 
-func find_animation_player_recursive(node: Node) -> AnimationPlayer:
+func _find_animation_player(node: Node) -> AnimationPlayer:
 	if node is AnimationPlayer:
 		return node
 	for child in node.get_children():