Add source kinds and the Learn tab with Learning sources (#2)

Every Source now has a kind: News, Learning or Fun. Curated Sources default
to News, and custom Sources persist their kind (ones saved before default
to News). Each kind has its own time window: News follows the 12/24/48 h
setting, Learning reaches back 14 days, Fun 3 days.

A new Learn tab between Briefing and Sources lists Learning articles with
the same paid/sponsored filters and reader view as Today. It is built from
a list of kinds so a Fun section can follow. Today and the Briefing only
use News. ByteByteGo is the first Learning source, on by default.

The home shell names its tabs instead of using hard-coded indexes.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

lib/ui/briefing_screen.dart

@@ -1,6 +1,7 @@
 import 'package:flutter/material.dart';
 
 import '../models/briefing.dart';
+import '../models/news_source.dart';
 import '../state/app_state.dart';
 import 'article_screen.dart';
 import 'briefing_history_screen.dart';
@@ -59,7 +60,7 @@ class BriefingScreen extends StatelessWidget {
     if (state.briefingLoading) {
       return EmptyState(
         icon: Icons.hourglass_top,
-        title: 'Reading ${state.visibleArticles.length} headlines…',
+        title: 'Reading ${state.articlesOf(SourceKind.news).length} headlines…',
         message: 'This usually takes 10-60 seconds.',
         action: const SizedBox(width: 160, child: LinearProgressIndicator()),
       );
@@ -69,7 +70,7 @@ class BriefingScreen extends StatelessWidget {
       icon: const Icon(Icons.auto_awesome),
       label: Text(state.loading
           ? 'Waiting for feeds…'
-          : 'Generate from ${state.visibleArticles.length} articles'),
+          : 'Generate from ${state.articlesOf(SourceKind.news).length} articles'),
     );
     if (briefing == null) {
       return EmptyState(

lib/ui/feed_screen.dart

@@ -25,13 +25,13 @@ class _FeedScreenState extends State<FeedScreen> {
       listenable: widget.state,
       builder: (context, _) {
         final state = widget.state;
-        final all = state.visibleArticles;
+        final all = state.articlesOf(SourceKind.news);
         final visible = all
             .where((a) => _language == null || a.source.language == _language)
             .where((a) => _sourceId == null || a.source.id == _sourceId)
             .toList();
         final sourcesInFeed = {for (final a in all) a.source.id: a.source};
-        final hidden = state.hiddenCount;
+        final hidden = state.hiddenCountOf(SourceKind.news);
 
         return Scaffold(
           appBar: AppBar(

lib/ui/home_shell.dart

@@ -3,9 +3,13 @@ import 'package:flutter/material.dart';
 import '../state/app_state.dart';
 import 'briefing_screen.dart';
 import 'feed_screen.dart';
+import 'learn_screen.dart';
 import 'settings_screen.dart';
 import 'sources_screen.dart';
 
+/// The tabs in the order they appear in the navigation bar.
+enum _Tab { today, briefing, learn, sources, settings }
+
 class HomeShell extends StatefulWidget {
   const HomeShell({super.key, required this.state});
 
@@ -16,20 +20,20 @@ class HomeShell extends StatefulWidget {
 }
 
 class _HomeShellState extends State<HomeShell> {
-  int _index = 0;
+  _Tab _tab = _Tab.today;
   bool _sourcesChanged = false;
 
-  void _select(int index) {
+  void _select(_Tab tab) {
     // A text field left focused in Settings would otherwise get focus back
     // (and open the keyboard) when returning from an article.
     FocusManager.instance.primaryFocus?.unfocus();
     // Source toggles only take effect on the next refresh; do it when the
     // user leaves the Sources tab.
-    if (_index == 2 && index != 2 && _sourcesChanged) {
+    if (_tab == _Tab.sources && tab != _Tab.sources && _sourcesChanged) {
       _sourcesChanged = false;
       widget.state.refresh();
     }
-    setState(() => _index = index);
+    setState(() => _tab = tab);
   }
 
   @override
@@ -37,20 +41,27 @@ class _HomeShellState extends State<HomeShell> {
     final state = widget.state;
     return Scaffold(
       body: IndexedStack(
-        index: _index,
+        index: _tab.index,
         children: [
-          FeedScreen(state: state),
-          BriefingScreen(state: state, openSettings: () => _select(3)),
-          SourcesScreen(state: state, onChanged: () => _sourcesChanged = true),
-          SettingsScreen(state: state),
-        ].indexed
+          for (final tab in _Tab.values)
             // Hidden tabs stay alive but must not hold or regain focus.
-            .map((e) => ExcludeFocus(excluding: e.$1 != _index, child: e.$2))
-            .toList(),
+            ExcludeFocus(
+              excluding: tab != _tab,
+              child: switch (tab) {
+                _Tab.today => FeedScreen(state: state),
+                _Tab.briefing => BriefingScreen(
+                    state: state, openSettings: () => _select(_Tab.settings)),
+                _Tab.learn => LearnScreen(state: state),
+                _Tab.sources =>
+                  SourcesScreen(state: state, onChanged: () => _sourcesChanged = true),
+                _Tab.settings => SettingsScreen(state: state),
+              },
+            ),
+        ],
       ),
       bottomNavigationBar: NavigationBar(
-        selectedIndex: _index,
-        onDestinationSelected: _select,
+        selectedIndex: _tab.index,
+        onDestinationSelected: (i) => _select(_Tab.values[i]),
         destinations: const [
           NavigationDestination(
               icon: Icon(Icons.newspaper_outlined),
@@ -60,6 +71,10 @@ class _HomeShellState extends State<HomeShell> {
               icon: Icon(Icons.auto_awesome_outlined),
               selectedIcon: Icon(Icons.auto_awesome),
               label: 'Briefing'),
+          NavigationDestination(
+              icon: Icon(Icons.school_outlined),
+              selectedIcon: Icon(Icons.school),
+              label: 'Learn'),
           NavigationDestination(
               icon: Icon(Icons.rss_feed_outlined),
               selectedIcon: Icon(Icons.rss_feed),

lib/ui/learn_screen.dart

@@ -0,0 +1,98 @@
+import 'package:flutter/material.dart';
+
+import '../models/news_source.dart';
+import '../state/app_state.dart';
+import 'article_screen.dart';
+import 'feed_screen.dart';
+
+/// Reading that keeps for days, from the Sources that aren't News: one
+/// section per kind, each with its own time window.
+class LearnScreen extends StatelessWidget {
+  const LearnScreen({super.key, required this.state});
+
+  final AppState state;
+
+  /// The sections, top to bottom.
+  static const kinds = [SourceKind.learning];
+
+  @override
+  Widget build(BuildContext context) {
+    return ListenableBuilder(
+      listenable: state,
+      builder: (context, _) => Scaffold(
+        appBar: AppBar(
+          title: const Text('Learn'),
+          actions: [
+            IconButton(
+              tooltip: 'Refresh',
+              onPressed: state.loading ? null : state.refresh,
+              icon: const Icon(Icons.refresh),
+            ),
+          ],
+        ),
+        body: Column(
+          children: [
+            if (state.loading) const LinearProgressIndicator(),
+            Expanded(
+              child: RefreshIndicator(
+                onRefresh: state.refresh,
+                child: ListView(
+                  padding: const EdgeInsets.fromLTRB(12, 0, 12, 24),
+                  children: [for (final kind in kinds) ..._section(context, kind)],
+                ),
+              ),
+            ),
+          ],
+        ),
+      ),
+    );
+  }
+
+  List<Widget> _section(BuildContext context, SourceKind kind) {
+    final theme = Theme.of(context);
+    final muted = theme.colorScheme.onSurfaceVariant;
+    final articles = state.articlesOf(kind);
+    final hidden = state.hiddenCountOf(kind);
+    final hasSources = state.enabledSources.any((s) => s.kind == kind);
+    return [
+      Padding(
+        padding: const EdgeInsets.fromLTRB(4, 16, 4, 8),
+        child: Column(
+          crossAxisAlignment: CrossAxisAlignment.start,
+          children: [
+            Text(kind.label,
+                style: theme.textTheme.titleMedium?.copyWith(color: theme.colorScheme.primary)),
+            Text(
+              '${articles.length} articles · last ${_describe(state.windowOf(kind))}'
+              '${hidden > 0 ? ' · $hidden paid/ads hidden' : ''}',
+              style: theme.textTheme.bodySmall?.copyWith(color: muted),
+            ),
+          ],
+        ),
+      ),
+      if (articles.isEmpty && !state.loading)
+        Padding(
+          padding: const EdgeInsets.fromLTRB(4, 8, 4, 16),
+          child: Text(
+            hasSources
+                ? 'Nothing new in this window. Pull down to refresh.'
+                : 'No ${kind.label} sources enabled. Turn some on in the Sources tab.',
+            style: theme.textTheme.bodyMedium?.copyWith(color: muted),
+          ),
+        ),
+      for (final article in articles)
+        Padding(
+          padding: const EdgeInsets.only(bottom: 8),
+          child: ArticleCard(
+            article: article,
+            hasSummary: state.summaries[article.id]?.text != null,
+            isPaid: state.paywall.isPaid(article),
+            onTap: () => openArticle(context, state, article),
+          ),
+        ),
+    ];
+  }
+
+  static String _describe(Duration window) =>
+      window.inHours < 72 ? '${window.inHours} h' : '${window.inDays} days';
+}