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>

lib/providers/api_client_provider.dart

@@ -4,13 +4,12 @@ import 'package:flutter_riverpod/flutter_riverpod.dart';
 
 import '../data/api/api_client.dart';
 import '../data/api/auth_api.dart';
-import '../data/api/briefing_api.dart';
 import '../data/api/chat_api.dart';
+import '../data/api/journal_api.dart';
 import '../data/api/knowledge_api.dart';
 import '../data/api/voice_api.dart';
 import '../data/api/milestones_api.dart';
 import '../data/api/events_api.dart';
-import '../data/api/news_api.dart';
 import '../data/api/notes_api.dart';
 import '../data/api/projects_api.dart';
 import '../data/api/quick_capture_api.dart';
@@ -97,8 +96,8 @@ final knowledgeRepositoryProvider = Provider<KnowledgeRepository>((ref) {
   return KnowledgeRepository(ref.watch(knowledgeApiProvider));
 });
 
-final briefingApiProvider = Provider<BriefingApi>((ref) {
-  return BriefingApi(ref.watch(dioProvider));
+final journalApiProvider = Provider<JournalApi>((ref) {
+  return JournalApi(ref.watch(dioProvider));
 });
 
 final settingsApiProvider = Provider<SettingsApi>((ref) {
@@ -113,10 +112,6 @@ final voiceRepositoryProvider = Provider<VoiceRepository>((ref) {
   return VoiceRepository(ref.watch(voiceApiProvider));
 });
 
-final newsApiProvider = Provider<NewsApi>((ref) {
-  return NewsApi(ref.watch(dioProvider));
-});
-
 final eventsApiProvider = Provider<EventsApi>((ref) {
   return EventsApi(ref.watch(dioProvider));
 });