add (very rough) gizmo, restructure Dart package into library, add EntityListWidget

lib/filament/widgets/ibl_rotation_slider.dart

@@ -0,0 +1,31 @@
+import 'dart:math';
+
+import 'package:flutter/material.dart';
+import 'package:flutter/widgets.dart';
+import 'package:flutter_filament/filament/filament_controller.dart';
+import 'package:vector_math/vector_math_64.dart' as v;
+
+class IblRotationSliderWidget extends StatefulWidget {
+  final FilamentController controller;
+
+  const IblRotationSliderWidget({super.key, required this.controller});
+  @override
+  State<StatefulWidget> createState() => _IblRotationSliderWidgetState();
+}
+
+class _IblRotationSliderWidgetState extends State<IblRotationSliderWidget> {
+  double _iblRotation = 0;
+  @override
+  Widget build(BuildContext context) {
+    return Slider(
+        value: _iblRotation,
+        onChanged: (value) {
+          _iblRotation = value;
+          setState(() {});
+          print(value);
+          var rotation = v.Matrix3.identity();
+          Matrix4.rotationY(value * 2 * pi).copyRotation(rotation);
+          widget.controller.rotateIbl(rotation);
+        });
+  }
+}