chore: initial release

lib/core/models/chat_message.dart

@@ -0,0 +1,23 @@
+import 'package:freezed_annotation/freezed_annotation.dart';
+
+part 'chat_message.freezed.dart';
+part 'chat_message.g.dart';
+
+@freezed
+sealed class ChatMessage with _$ChatMessage {
+  const factory ChatMessage({
+    required String id,
+    required String role, // 'user', 'assistant', 'system'
+    required String content,
+    required DateTime timestamp,
+    String? model,
+    @Default(false) bool isStreaming,
+    List<String>? attachmentIds,
+    Map<String, dynamic>? metadata,
+    List<Map<String, dynamic>>? sources,
+    Map<String, dynamic>? usage,
+  }) = _ChatMessage;
+
+  factory ChatMessage.fromJson(Map<String, dynamic> json) =>
+      _$ChatMessageFromJson(json);
+}