Merge feature/source-kinds into ticket/3-fun-section (#3)

Keeps the Learning catalog from #6 and puts the Fun group after it, in the
catalog and the README. Adds the end-to-end check #4 left for Fun: a custom
Fun feed added on the Sources tab shows up in the Learn tab's Fun section,
not in Today.

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

lib/data/default_sources.dart

@@ -212,6 +212,155 @@ const defaultSources = <NewsSource>[
     description: 'System design explained with diagrams',
     enabledByDefault: true,
   ),
+  NewsSource(
+    id: 'systemdesignone',
+    name: 'System Design One',
+    feedUrl: 'https://newsletter.systemdesign.one/feed',
+    homepage: 'https://newsletter.systemdesign.one',
+    language: SourceLanguage.en,
+    kind: SourceKind.learning,
+    description: 'System design case studies of real systems',
+    enabledByDefault: true,
+  ),
+  NewsSource(
+    id: 'pragmaticengineer-blog',
+    name: 'The Pragmatic Engineer (blog)',
+    feedUrl: 'https://blog.pragmaticengineer.com/rss/',
+    homepage: 'https://blog.pragmaticengineer.com',
+    language: SourceLanguage.en,
+    kind: SourceKind.learning,
+    description: 'How big tech and startups build software (free posts)',
+    enabledByDefault: true,
+  ),
+  NewsSource(
+    id: 'martinfowler',
+    name: 'Martin Fowler',
+    feedUrl: 'https://martinfowler.com/feed.atom',
+    homepage: 'https://martinfowler.com',
+    language: SourceLanguage.en,
+    kind: SourceKind.learning,
+    description: 'Software architecture, refactoring, delivery practices',
+    enabledByDefault: true,
+  ),
+  NewsSource(
+    id: 'juliaevans',
+    name: 'Julia Evans',
+    feedUrl: 'https://jvns.ca/atom.xml',
+    homepage: 'https://jvns.ca',
+    language: SourceLanguage.en,
+    kind: SourceKind.learning,
+    description: 'Systems, networking and Unix tools, explained plainly',
+    enabledByDefault: true,
+  ),
+  NewsSource(
+    id: 'danluu',
+    name: 'Dan Luu',
+    feedUrl: 'https://danluu.com/atom.xml',
+    homepage: 'https://danluu.com',
+    language: SourceLanguage.en,
+    kind: SourceKind.learning,
+    description: 'Long, data-driven essays on computers and engineering',
+    enabledByDefault: true,
+  ),
+  NewsSource(
+    id: 'cloudflare-blog',
+    name: 'The Cloudflare Blog',
+    feedUrl: 'https://blog.cloudflare.com/rss/',
+    homepage: 'https://blog.cloudflare.com',
+    language: SourceLanguage.en,
+    kind: SourceKind.learning,
+    description: 'Networking, security and incident write-ups in depth',
+    enabledByDefault: true,
+  ),
+  NewsSource(
+    id: 'netflix-techblog',
+    name: 'Netflix Technology Blog',
+    feedUrl: 'https://netflixtechblog.com/feed',
+    homepage: 'https://netflixtechblog.com',
+    language: SourceLanguage.en,
+    kind: SourceKind.learning,
+    description: 'Distributed systems, data and streaming at scale',
+    enabledByDefault: true,
+  ),
+  NewsSource(
+    id: 'meta-engineering',
+    name: 'Engineering at Meta',
+    feedUrl: 'https://engineering.fb.com/feed/',
+    homepage: 'https://engineering.fb.com',
+    language: SourceLanguage.en,
+    kind: SourceKind.learning,
+    description: 'Infrastructure, AI and production engineering at Meta',
+    enabledByDefault: true,
+  ),
+  NewsSource(
+    id: 'github-engineering',
+    name: 'GitHub Blog: Engineering',
+    feedUrl: 'https://github.blog/engineering/feed/',
+    homepage: 'https://github.blog/engineering/',
+    language: SourceLanguage.en,
+    kind: SourceKind.learning,
+    description: 'How GitHub builds and runs GitHub',
+    enabledByDefault: true,
+  ),
+  NewsSource(
+    id: 'latent-space',
+    name: 'Latent Space',
+    feedUrl: 'https://www.latent.space/feed',
+    homepage: 'https://www.latent.space',
+    language: SourceLanguage.en,
+    kind: SourceKind.learning,
+    description: 'AI engineering: interviews and deep dives',
+    enabledByDefault: true,
+  ),
+  NewsSource(
+    id: 'import-ai',
+    name: 'Import AI',
+    feedUrl: 'https://importai.substack.com/feed',
+    homepage: 'https://importai.substack.com',
+    language: SourceLanguage.en,
+    kind: SourceKind.learning,
+    description: 'Weekly AI research digest by Jack Clark',
+    enabledByDefault: true,
+  ),
+  NewsSource(
+    id: 'interconnects',
+    name: 'Interconnects',
+    feedUrl: 'https://www.interconnects.ai/feed',
+    homepage: 'https://www.interconnects.ai',
+    language: SourceLanguage.en,
+    kind: SourceKind.learning,
+    description: 'Language model training and research, analysed',
+    enabledByDefault: true,
+  ),
+  NewsSource(
+    id: 'ahead-of-ai',
+    name: 'Ahead of AI',
+    feedUrl: 'https://magazine.sebastianraschka.com/feed',
+    homepage: 'https://magazine.sebastianraschka.com',
+    language: SourceLanguage.en,
+    kind: SourceKind.learning,
+    description: 'LLM research explained, by Sebastian Raschka',
+    enabledByDefault: true,
+  ),
+  NewsSource(
+    id: 'lilianweng',
+    name: 'Lilian Weng',
+    feedUrl: 'https://lilianweng.github.io/index.xml',
+    homepage: 'https://lilianweng.github.io',
+    language: SourceLanguage.en,
+    kind: SourceKind.learning,
+    description: 'Thorough surveys of machine learning topics',
+    enabledByDefault: true,
+  ),
+  NewsSource(
+    id: 'infoq',
+    name: 'InfoQ',
+    feedUrl: 'https://feed.infoq.com/',
+    homepage: 'https://www.infoq.com',
+    language: SourceLanguage.en,
+    kind: SourceKind.learning,
+    description: 'Software architecture and engineering talks, high volume',
+  ),
 
   // --- Fun ----------------------------------------------------------------
   NewsSource(

lib/ui/sources_screen.dart

@@ -40,29 +40,7 @@ class SourcesScreen extends StatelessWidget {
           body: ListView(
             padding: const EdgeInsets.only(bottom: 96),
             children: [
-              for (final lang in SourceLanguage.values) ...[
-                Padding(
-                  padding: const EdgeInsets.fromLTRB(16, 16, 16, 4),
-                  child: Text('${lang.flag}  ${lang.label}',
-                      style: theme.textTheme.titleSmall
-                          ?.copyWith(color: theme.colorScheme.primary)),
-                ),
-                for (final source in state.allSources.where((s) => s.language == lang))
-                  _SourceTile(
-                    source: source,
-                    enabled: state.enabledSourceIds.contains(source.id),
-                    onToggle: (v) {
-                      state.setSourceEnabled(source, v);
-                      onChanged();
-                    },
-                    onDelete: source.isCustom
-                        ? () {
-                            state.removeCustomSource(source);
-                            onChanged();
-                          }
-                        : null,
-                  ),
-              ],
+              for (final kind in SourceKind.values) ..._kindSection(context, kind),
             ],
           ),
         );
@@ -70,6 +48,44 @@ class SourcesScreen extends StatelessWidget {
     );
   }
 
+  /// One section per kind, split by language. Kinds and languages without
+  /// Sources are left out instead of showing an empty header.
+  List<Widget> _kindSection(BuildContext context, SourceKind kind) {
+    final theme = Theme.of(context);
+    final sources = state.allSources.where((s) => s.kind == kind).toList();
+    if (sources.isEmpty) return const [];
+    return [
+      Padding(
+        padding: const EdgeInsets.fromLTRB(16, 24, 16, 0),
+        child: Text(kind.label, style: theme.textTheme.titleMedium),
+      ),
+      for (final lang in SourceLanguage.values)
+        if (sources.any((s) => s.language == lang)) ...[
+          Padding(
+            padding: const EdgeInsets.fromLTRB(16, 12, 16, 4),
+            child: Text('${lang.flag}  ${lang.label}',
+                style: theme.textTheme.titleSmall
+                    ?.copyWith(color: theme.colorScheme.primary)),
+          ),
+          for (final source in sources.where((s) => s.language == lang))
+            _SourceTile(
+              source: source,
+              enabled: state.enabledSourceIds.contains(source.id),
+              onToggle: (v) {
+                state.setSourceEnabled(source, v);
+                onChanged();
+              },
+              onDelete: source.isCustom
+                  ? () {
+                      state.removeCustomSource(source);
+                      onChanged();
+                    }
+                  : null,
+            ),
+        ],
+    ];
+  }
+
   Future<void> _addFeed(BuildContext context) async {
     final added = await showDialog<bool>(
       context: context,
@@ -134,6 +150,7 @@ class _AddFeedDialogState extends State<_AddFeedDialog> {
   final _name = TextEditingController();
   final _url = TextEditingController();
   SourceLanguage _language = SourceLanguage.de;
+  SourceKind _kind = SourceKind.news;
   bool _busy = false;
   String? _error;
 
@@ -156,7 +173,7 @@ class _AddFeedDialogState extends State<_AddFeedDialog> {
       _error = null;
     });
     final error = await widget.state
-        .addCustomSource(name: name, feedUrl: url, language: _language);
+        .addCustomSource(name: name, feedUrl: url, language: _language, kind: _kind);
     if (!mounted) return;
     if (error == null) {
       Navigator.pop(context, true);
@@ -199,6 +216,15 @@ class _AddFeedDialogState extends State<_AddFeedDialog> {
               selected: {_language},
               onSelectionChanged: (s) => setState(() => _language = s.first),
             ),
+            const SizedBox(height: 12),
+            SegmentedButton<SourceKind>(
+              segments: [
+                for (final k in SourceKind.values)
+                  ButtonSegment(value: k, label: Text(k.label)),
+              ],
+              selected: {_kind},
+              onSelectionChanged: (s) => setState(() => _kind = s.first),
+            ),
             if (_error != null) ...[
               const SizedBox(height: 12),
               Text(_error!, style: TextStyle(color: Theme.of(context).colorScheme.error)),