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.

debug/test_gltf_api.gd

@@ -0,0 +1,49 @@
+extends SceneTree
+
+func _init():
+    print("=== GLTFDocument API Test ===")
+    
+    var path = "res://assets/characters/skins/miku_rigged_animated.glb"
+    
+    var file = FileAccess.open(path, FileAccess.READ)
+    var bytes = file.get_buffer(file.get_length())
+    file.close()
+    
+    var gltf = GLTFDocument.new()
+    var state = GLTFState.new()
+    
+    var err = gltf.append_from_buffer(bytes, "", state)
+    print("append_from_buffer: %d" % err)
+    
+    if err == OK:
+        # List all methods
+        var methods = gltf.get_method_list()
+        print("Total methods: %d" % methods.size())
+        for m in methods:
+            var n = m.name
+            if n.contains("anim") or n.contains("mesh") or n.contains("scene") or n.contains("generate") or n.contains("get_") or n.contains("instantiate"):
+                print("  %s" % n)
+        
+        # Try generate_scene
+        if gltf.has_method("generate_scene"):
+            var scene = gltf.generate_scene(state)
+            if scene:
+                print("Scene: %s" % scene.name)
+                get_root().add_child(scene)
+            else:
+                print("generate_scene returned null")
+        else:
+            print("No generate_scene method")
+        
+        # Try instantiate  
+        if gltf.has_method("instantiate"):
+            var node = gltf.instantiate(state)
+            if node:
+                print("Instantiated: %s" % node.name)
+                get_root().add_child(node)
+            else:
+                print("instantiate returned null")
+        else:
+            print("No instantiate method")
+    
+    quit()

debug/test_gltf_loader.gd

@@ -0,0 +1,38 @@
+extends SceneTree
+
+func _init():
+    print("=== GLTFDocument Test ===")
+    
+    var path = "res://assets/characters/skins/miku_rigged_animated.glb"
+    
+    if not FileAccess.file_exists(path):
+        print("File not found")
+        quit()
+        return
+    
+    var file = FileAccess.open(path, FileAccess.READ)
+    var bytes = file.get_buffer(file.get_length())
+    file.close()
+    
+    print("Read %d bytes" % bytes.size())
+    
+    var gltf = GLTFDocument.new()
+    var state = GLTFState.new()
+    
+    var err = gltf.append_from_buffer(bytes, "", state)
+    print("append_from_buffer returned: %d" % err)
+    
+    if err == OK:
+        print("Animations: %d" % gltf.get_animation_count())
+        print("Meshes: %d" % gltf.get_mesh_count())
+        
+        var scene = gltf.generate_scene(state)
+        if scene:
+            print("Scene: %s" % scene.name)
+            get_root().add_child(scene)
+        else:
+            print("Failed to generate scene")
+    else:
+        print("Failed to parse")
+    
+    quit()

debug/test_level_builder.gd

@@ -436,6 +436,7 @@ func _spawn_player(pid: int) -> CharacterBody3D:
 		skinned.scale_factor = 1.0  # Already scaled to 1.8m in Blender
 		skinned.position = Vector3.ZERO  # Model origin = player origin
 		player.add_child(skinned)
+		print("TestLevelBuilder: added SkinnedModel for player 1")
 	else:
 		# Default: procedural humanoid
 		var humanoid = load("res://characters/humanoid_model.gd").new()

debug/test_runtime_load.gd

@@ -0,0 +1,36 @@
+extends SceneTree
+
+func _init():
+    print("=== Test GLB Load ===")
+    
+    var path = "res://assets/characters/skins/miku_rigged_animated.glb"
+    
+    # Read GLB
+    var file = FileAccess.open(path, FileAccess.READ)
+    var bytes = file.get_buffer(file.get_length())
+    file.close()
+    print("Read %d bytes" % bytes.size())
+    
+    # Parse
+    var gltf = GLTFDocument.new()
+    var state = GLTFState.new()
+    var err = gltf.append_from_buffer(bytes, "", state)
+    print("Parse result: %d" % err)
+    
+    if err == OK:
+        var scene = gltf.generate_scene(state)
+        if scene:
+            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())
+                if child is AnimationPlayer:
+                    print("    Animations: %s" % child.get_animation_list())
+            get_root().add_child(scene)
+            print("Scene added to tree!")
+        else:
+            print("Failed to generate scene")
+    
+    quit()