feat: Enable direct chat initiation from agent network, improve GIF rendering in chat, and fix message order and webview authentication.

lib/features/messaging/data/messaging_repository.dart

@@ -49,6 +49,24 @@ class MessagingRepository {
     }
   }
 
+  /// POST /messages/conversations (agent → user)
+  Future<Conversation> startConversationWithUser(String userId) async {
+    try {
+      final response = await _dio.post(
+        ApiConstants.conversations,
+        data: {'userId': userId},
+      );
+      return Conversation.fromJson(
+          response.data['data'] as Map<String, dynamic>);
+    } on DioException catch (e) {
+      if (e.error is ApiException) throw e.error as ApiException;
+      throw ApiException(
+        message: e.message ?? 'Failed to start conversation',
+        statusCode: e.response?.statusCode,
+      );
+    }
+  }
+
   /// GET /messages/conversations/:id
   Future<Conversation> getConversation(String id) async {
     try {