feat(journal): replace briefing surface with journal; remove news/RSS

The backend retired /api/briefing/* and the RSS feature entirely. This
Flutter change mirrors what landed web-side: rename the briefing surface
to journal, repoint at /api/journal/*, and drop the news/RSS UI since
its endpoints no longer exist.

New (mirrors briefing structure with adapted shapes):
- lib/data/api/journal_api.dart — getToday, getDay, getDays, triggerPrep
- lib/data/models/journal_day.dart — {day_date, conversation, messages}
- lib/providers/journal_provider.dart — async notifier, sendReply, polling,
  silent refresh, regeneratePrep. Mirrors the briefing notifier 1:1
- lib/widgets/journal_prep_card.dart — adapted briefing_digest_card
- lib/screens/journal/journal_screen.dart — adapted briefing_screen,
  weather card preserved (rendered from msg_metadata.sections.weather
  on the daily-prep assistant message). News cards / RSS reactions /
  article-discuss removed
- lib/screens/journal/journal_history_screen.dart — past days picker
  pulls /api/journal/days, drills into /api/journal/day/<iso>

Wiring:
- Routes.briefing → Routes.journal (constants.dart)
- Routes.news removed
- briefingApiProvider → journalApiProvider (api_client_provider.dart)
- newsApiProvider removed
- app.dart: shell tab "Briefing" → "Journal"; News destination removed
  from nav rail, bottom nav, and the More sheet
- splash_screen.dart and login_screen.dart: redirect Routes.journal
  instead of Routes.briefing
- chat_api.dart: drop openArticleInChat (calls deleted /api/chat/from-article)
- settings_provider.dart: drop rssEnabled getter and rssEnabledProvider

Deleted:
- lib/screens/briefing/ (whole directory)
- lib/screens/news/ (whole directory)
- lib/data/api/briefing_api.dart, news_api.dart
- lib/data/models/briefing_conversation.dart, briefing_feed.dart, news_item.dart
- lib/providers/briefing_provider.dart, news_provider.dart
- lib/widgets/briefing_digest_card.dart, news_card.dart
- test cases for NewsItem and BriefingFeed in test/widget_test.dart

flutter analyze: 0 issues.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

test/widget_test.dart

@@ -3,8 +3,6 @@ import 'package:fabled_app/data/api/voice_api.dart';
 import 'package:fabled_app/providers/voice_provider.dart';
 import 'package:fabled_app/data/models/knowledge_item.dart';
 import 'package:fabled_app/data/models/note.dart';
-import 'package:fabled_app/data/models/news_item.dart';
-import 'package:fabled_app/data/models/briefing_feed.dart';
 import 'package:flutter_test/flutter_test.dart';
 
 void main() {
@@ -150,47 +148,6 @@ void main() {
     });
   });
 
-  group('NewsItem.fromJson', () {
-    test('parses all fields', () {
-      final json = {
-        'id': 42,
-        'title': 'Big news',
-        'url': 'https://example.com/article',
-        'snippet': 'A short summary.',
-        'source': 'Example News',
-        'published_at': '2026-01-15T10:00:00',
-        'topics': ['tech', 'ai'],
-        'reaction': 'up',
-      };
-      final item = NewsItem.fromJson(json);
-      expect(item.id, equals(42));
-      expect(item.title, equals('Big news'));
-      expect(item.url, equals('https://example.com/article'));
-      expect(item.snippet, equals('A short summary.'));
-      expect(item.source, equals('Example News'));
-      expect(item.publishedAt, equals(DateTime.parse('2026-01-15T10:00:00')));
-      expect(item.topics, equals(['tech', 'ai']));
-      expect(item.reaction, equals('up'));
-    });
-
-    test('handles null published_at and reaction', () {
-      final json = {
-        'id': 1,
-        'title': '',
-        'url': '',
-        'snippet': '',
-        'source': '',
-        'published_at': null,
-        'topics': <dynamic>[],
-        'reaction': null,
-      };
-      final item = NewsItem.fromJson(json);
-      expect(item.publishedAt, isNull);
-      expect(item.reaction, isNull);
-      expect(item.topics, isEmpty);
-    });
-  });
-
   group('CalendarEvent.fromJson', () {
     test('parses all fields', () {
       final json = {
@@ -250,30 +207,4 @@ void main() {
     });
   });
 
-  group('BriefingFeed.fromJson', () {
-    test('parses all fields', () {
-      final json = {
-        'id': 7,
-        'title': 'Hacker News',
-        'url': 'https://news.ycombinator.com/rss',
-        'category': 'tech',
-      };
-      final feed = BriefingFeed.fromJson(json);
-      expect(feed.id, equals(7));
-      expect(feed.title, equals('Hacker News'));
-      expect(feed.url, equals('https://news.ycombinator.com/rss'));
-      expect(feed.category, equals('tech'));
-    });
-
-    test('handles null category', () {
-      final json = {
-        'id': 8,
-        'title': 'Feed',
-        'url': 'https://example.com/rss',
-        'category': null,
-      };
-      final feed = BriefingFeed.fromJson(json);
-      expect(feed.category, isNull);
-    });
-  });
 }