feat: add NewsItem and BriefingFeed models with tests

lib/data/models/briefing_feed.dart

@@ -0,0 +1,20 @@
+class BriefingFeed {
+  final int id;
+  final String title;
+  final String url;
+  final String? category;
+
+  const BriefingFeed({
+    required this.id,
+    required this.title,
+    required this.url,
+    this.category,
+  });
+
+  factory BriefingFeed.fromJson(Map<String, dynamic> json) => BriefingFeed(
+        id: json['id'] as int,
+        title: json['title'] as String? ?? '',
+        url: json['url'] as String? ?? '',
+        category: json['category'] as String?,
+      );
+}

lib/data/models/news_item.dart

@@ -0,0 +1,37 @@
+class NewsItem {
+  final int id;
+  final String title;
+  final String url;
+  final String snippet;
+  final String source;
+  final DateTime? publishedAt;
+  final List<String> topics;
+  final String? reaction;
+
+  const NewsItem({
+    required this.id,
+    required this.title,
+    required this.url,
+    required this.snippet,
+    required this.source,
+    this.publishedAt,
+    required this.topics,
+    this.reaction,
+  });
+
+  factory NewsItem.fromJson(Map<String, dynamic> json) => NewsItem(
+        id: json['id'] as int,
+        title: json['title'] as String? ?? '',
+        url: json['url'] as String? ?? '',
+        snippet: json['snippet'] as String? ?? '',
+        source: json['source'] as String? ?? '',
+        publishedAt: json['published_at'] != null
+            ? DateTime.tryParse(json['published_at'] as String)
+            : null,
+        topics: (json['topics'] as List<dynamic>?)
+                ?.cast<String>()
+                .toList() ??
+            [],
+        reaction: json['reaction'] as String?,
+      );
+}