fix(characters): preserve all animation tracks in GLTF runtime loading

remove_immutable_tracks=true (default) strips bone tracks where keyframes
match rest pose, removing 80%+ of tracks and causing T-pose.
Editor import uses false; runtime must match.

Closes T-pose bug where animations reported playing but model stayed rigid.

characters/glb_loader.gd

@@ -40,8 +40,9 @@ static func load(glb_path: String) -> Node3D:
     print("  Animations: %d" % gltf.get_animation_count())
     print("  Meshes: %d" % gltf.get_mesh_count())
     
-    # Generate scene
-    var scene = gltf.generate_scene(state)
+    # Generate scene — remove_immutable_tracks=false preserves all bone
+    # animation tracks (default true strips tracks where rest==pose → T-pose).
+    var scene = gltf.generate_scene(state, 30, false, false)
     if not scene:
         print("GLBLoader: failed to generate scene")
         return null