feat(ai-scribe): reorganize abstractions and update dialog modal UI

lib/features/composer/presentation/mixin/text_selection_mixin.dart

@@ -0,0 +1,79 @@
+import 'package:flutter/material.dart';
+
+typedef OnTextSelectionChanged = Function(TextSelectionData?);
+
+class TextSelectionData {
+  final bool hasSelection;
+  final String? selectedText;
+  final TextSelectionCoordinates? coordinates;
+
+  const TextSelectionData({
+    required this.hasSelection,
+    this.selectedText,
+    this.coordinates,
+  });
+
+  factory TextSelectionData.empty() {
+    return const TextSelectionData(hasSelection: false);
+  }
+
+  factory TextSelectionData.fromMap(Map<dynamic, dynamic> data) {
+    try {
+      final hasSelection = data['hasSelection'] as bool? ?? false;
+
+      if (!hasSelection) {
+        return TextSelectionData.empty();
+      }
+
+      final selectedText = data['selectedText'] as String?;
+      final coordinatesData = data['coordinates'];
+
+      if (coordinatesData != null && selectedText != null) {
+        final coordinates = TextSelectionCoordinates.fromMap(coordinatesData);
+        return TextSelectionData(
+          hasSelection: true,
+          selectedText: selectedText,
+          coordinates: coordinates,
+        );
+      }
+
+      return TextSelectionData.empty();
+    } catch (e) {
+      return TextSelectionData.empty();
+    }
+  }
+}
+
+class TextSelectionCoordinates {
+  final double x;
+  final double y;
+  final double width;
+  final double height;
+
+  const TextSelectionCoordinates({
+    required this.x,
+    required this.y,
+    required this.width,
+    required this.height,
+  });
+
+  factory TextSelectionCoordinates.fromMap(Map<dynamic, dynamic> data) {
+    return TextSelectionCoordinates(
+      x: (data['x'] as num?)?.toDouble() ?? 0.0,
+      y: (data['y'] as num?)?.toDouble() ?? 0.0,
+      width: (data['width'] as num?)?.toDouble() ?? 0.0,
+      height: (data['height'] as num?)?.toDouble() ?? 0.0,
+    );
+  }
+
+  Offset get position => Offset(x, y);
+}
+
+mixin TextSelectionMixin<T extends StatefulWidget> on State<T> {
+  OnTextSelectionChanged? get onSelectionChanged => null;
+
+  void handleSelectionChange(Map<dynamic, dynamic> data) {
+    final selectionData = TextSelectionData.fromMap(data);
+    onSelectionChanged?.call(selectionData);
+  }
+}