feat: weather card and RSS reactions in briefing screen

- Parse metadata field on Message model (weather, rss_item_ids)
- Add WeatherCard widget: location, current temp, condition, today hi/lo,
  delta from yesterday, scrollable 3-day forecast strip
- BriefingScreen shows WeatherCard above the first assistant message that
  carries weather metadata (mirrors web BriefingView.vue behaviour)
- RSS reaction buttons (👍/👎) shown below assistant messages with
  rss_item_ids; optimistic toggle with rollback on failure
- Add postRssReaction / deleteRssReaction to BriefingApi

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

lib/data/api/briefing_api.dart

@@ -59,4 +59,23 @@ class BriefingApi {
       throw dioToApp(e);
     }
   }
+
+  /// POST /api/briefing/rss-reactions  body: {rss_item_id, reaction: "up"|"down"}
+  Future<void> postRssReaction(int rssItemId, String reaction) async {
+    try {
+      await _dio.post('/api/briefing/rss-reactions',
+          data: {'rss_item_id': rssItemId, 'reaction': reaction});
+    } on DioException catch (e) {
+      throw dioToApp(e);
+    }
+  }
+
+  /// DELETE /api/briefing/rss-reactions/{rssItemId}
+  Future<void> deleteRssReaction(int rssItemId) async {
+    try {
+      await _dio.delete('/api/briefing/rss-reactions/$rssItemId');
+    } on DioException catch (e) {
+      throw dioToApp(e);
+    }
+  }
 }