feat(settings): collapse language list into a picker

The flat list of 6 languages plus 'system' dominated Settings. Replace it
with a single tile showing the current language, opening a bottom-sheet
picker (all languages + 'System language'). Resolve LocaleStore defensively
so the screen renders in DI-less widget tests.

apps/app_seeds/lib/ui/settings_screen.dart

@@ -20,51 +20,12 @@ class SettingsScreen extends StatelessWidget {
   @override
   Widget build(BuildContext context) {
     final t = context.t;
-    // Compare the full locale (not just the language code) so `es` and the
-    // Asturian `es-AST` — which share the `es` language — are told apart.
-    final current = TranslationProvider.of(context).locale;
-    void pick(AppLocale locale) =>
-        (localeStore ?? getIt<LocaleStore>()).setLocale(locale);
     return Scaffold(
       appBar: AppBar(title: Text(t.menu.settings)),
       body: ListView(
         children: [
           _SectionHeader(t.settings.language),
-          _LanguageTile(
-            label: t.settings.langEs,
-            selected: current == AppLocale.es,
-            onTap: () => pick(AppLocale.es),
-          ),
-          _LanguageTile(
-            label: t.settings.langAst,
-            selected: current == AppLocale.ast,
-            onTap: () => pick(AppLocale.ast),
-          ),
-          _LanguageTile(
-            label: t.settings.langEn,
-            selected: current == AppLocale.en,
-            onTap: () => pick(AppLocale.en),
-          ),
-          _LanguageTile(
-            label: t.settings.langPt,
-            selected: current == AppLocale.pt,
-            onTap: () => pick(AppLocale.pt),
-          ),
-          _LanguageTile(
-            label: t.settings.langFr,
-            selected: current == AppLocale.fr,
-            onTap: () => pick(AppLocale.fr),
-          ),
-          _LanguageTile(
-            label: t.settings.langDe,
-            selected: current == AppLocale.de,
-            onTap: () => pick(AppLocale.de),
-          ),
-          ListTile(
-            leading: const Icon(Icons.smartphone_outlined),
-            title: Text(t.settings.systemLanguage),
-            onTap: () => (localeStore ?? getIt<LocaleStore>()).useDeviceLocale(),
-          ),
+          _LanguageSelector(localeStore: localeStore),
           const Divider(),
           _SectionHeader(t.backup.title),
           BackupSection(service: exportImport),
@@ -89,6 +50,136 @@ class SettingsScreen extends StatelessWidget {
   }
 }
 
+/// The full ordered list of app languages, paired with their endonym label.
+/// One source of truth for both the current-choice subtitle and the picker.
+List<(AppLocale, String)> _languages(Translations t) => [
+  (AppLocale.es, t.settings.langEs),
+  (AppLocale.ast, t.settings.langAst),
+  (AppLocale.en, t.settings.langEn),
+  (AppLocale.pt, t.settings.langPt),
+  (AppLocale.fr, t.settings.langFr),
+  (AppLocale.de, t.settings.langDe),
+];
+
+/// A single tile showing the active language; tapping opens a picker with all
+/// languages plus "System language" (follow the device). A `null` saved value
+/// means the user follows the device language — the app still resolves to some
+/// concrete locale, but the picker must show "System language" as the choice.
+class _LanguageSelector extends StatefulWidget {
+  const _LanguageSelector({this.localeStore});
+
+  final LocaleStore? localeStore;
+
+  @override
+  State<_LanguageSelector> createState() => _LanguageSelectorState();
+}
+
+class _LanguageSelectorState extends State<_LanguageSelector> {
+  /// Prefer the injected store; otherwise fall back to the locator, but only if
+  /// it actually has one registered — widget tests may pump this screen with no
+  /// DI set up, and reading the current language must not crash there.
+  LocaleStore? get _store =>
+      widget.localeStore ??
+      (getIt.isRegistered<LocaleStore>() ? getIt<LocaleStore>() : null);
+
+  /// The user's explicit choice, or null when following the device language.
+  AppLocale? _saved;
+  bool _loaded = false;
+
+  @override
+  void initState() {
+    super.initState();
+    _store?.saved().then((locale) {
+      if (!mounted) return;
+      setState(() {
+        _saved = locale;
+        _loaded = true;
+      });
+    });
+  }
+
+  Future<void> _select(AppLocale? locale) async {
+    final store = _store;
+    if (store == null) return;
+    if (locale == null) {
+      await store.useDeviceLocale();
+    } else {
+      await store.setLocale(locale);
+    }
+    if (mounted) setState(() => _saved = locale);
+  }
+
+  @override
+  Widget build(BuildContext context) {
+    final t = context.t;
+    // The tile shows the current language by its endonym. When following the
+    // device language, the title is still the resolved language and a subtitle
+    // makes the "System language" mode explicit.
+    final resolved = TranslationProvider.of(context).locale;
+    final isDevice = _loaded && _saved == null;
+    final label = _labelFor(t, _loaded && _saved != null ? _saved! : resolved);
+    return ListTile(
+      key: const Key('settings.language'),
+      leading: const Icon(Icons.translate, color: seedGreen),
+      title: Text(label),
+      subtitle: isDevice ? Text(t.settings.systemLanguage) : null,
+      trailing: const Icon(Icons.chevron_right),
+      onTap: () => _openPicker(context),
+    );
+  }
+
+  String _labelFor(Translations t, AppLocale locale) {
+    for (final (l, label) in _languages(t)) {
+      if (l == locale) return label;
+    }
+    return locale.languageCode;
+  }
+
+  Future<void> _openPicker(BuildContext context) async {
+    final t = context.t;
+    final selection = await showModalBottomSheet<Object?>(
+      context: context,
+      showDragHandle: true,
+      builder: (context) {
+        return SafeArea(
+          child: ListView(
+            shrinkWrap: true,
+            children: [
+              for (final (locale, label) in _languages(t))
+                ListTile(
+                  title: Text(label),
+                  trailing: _saved == locale
+                      ? const Icon(Icons.check, color: seedGreen)
+                      : null,
+                  onTap: () => Navigator.pop(context, locale),
+                ),
+              const Divider(),
+              ListTile(
+                leading: const Icon(Icons.smartphone_outlined),
+                title: Text(t.settings.systemLanguage),
+                trailing: _saved == null
+                    ? const Icon(Icons.check, color: seedGreen)
+                    : null,
+                // Use a sentinel so "System language" (null) is distinct from
+                // "nothing tapped" (also null from a dismissed sheet).
+                onTap: () => Navigator.pop(context, _deviceSentinel),
+              ),
+            ],
+          ),
+        );
+      },
+    );
+    if (selection == null) return; // dismissed without choosing
+    await _select(
+      identical(selection, _deviceSentinel) ? null : selection as AppLocale,
+    );
+  }
+}
+
+/// Distinguishes an explicit "System language" pick from a dismissed sheet,
+/// since both would otherwise arrive as `null`.
+const Object _deviceSentinel = Object();
+
 class _SectionHeader extends StatelessWidget {
   const _SectionHeader(this.text);
 
@@ -109,24 +200,3 @@ class _SectionHeader extends StatelessWidget {
     );
   }
 }
-
-class _LanguageTile extends StatelessWidget {
-  const _LanguageTile({
-    required this.label,
-    required this.selected,
-    required this.onTap,
-  });
-
-  final String label;
-  final bool selected;
-  final VoidCallback onTap;
-
-  @override
-  Widget build(BuildContext context) {
-    return ListTile(
-      title: Text(label),
-      trailing: selected ? const Icon(Icons.check, color: seedGreen) : null,
-      onTap: onTap,
-    );
-  }
-}

apps/app_seeds/test/ui/asturian_locale_test.dart

@@ -52,6 +52,9 @@ void main() {
     expect(find.text('Language'), findsOneWidget);
     expect(materialLocale.languageCode, 'en');
 
+    // Open the language picker, then choose Asturian.
+    await tester.tap(find.byKey(const Key('settings.language')));
+    await tester.pumpAndSettle();
     await tester.tap(find.text('Asturianu'));
     await tester.pumpAndSettle();
 

apps/app_seeds/test/ui/rtl_smoke_test.dart

@@ -93,6 +93,9 @@ void main() {
     );
     await tester.pumpAndSettle();
 
+    // The language selector opens a picker listing every language.
+    await tester.tap(find.byKey(const Key('settings.language')));
+    await tester.pumpAndSettle();
     expect(find.text('Português'), findsOneWidget);
     await disposeTree(tester);
   });