feat(studio): app-wide i18n via flutter_localizations (v0.24.0)

Replaces the Store-only DE/EN toggle with an app-wide one
parked in the sidebar footer next to the theme button.
Pressing it flips every translated string at once: nav
labels, page titles, common buttons, the bilingual
store-index content.

Implementation:
- Adds `flutter_localizations` + `intl` to pubspec, plus
  `flutter.generate: true` so `flutter gen-l10n` runs in the
  build pipeline.
- ARB sources at `lib/l10n/app_en.arb` and `app_de.arb`. The
  EN file is the template; DE carries the German strings.
  Initial coverage: navigation, common buttons, page titles,
  channels / store / audit / modules / approvals headers,
  hub-unreachable copy, MCP + n8n panel headers + hints.
  Rest of the UI strings are still English-literal — those
  fall in incrementally as we touch each surface.
- Generated `AppLocalizations` lives at
  `lib/l10n/app_localizations*.dart` (regenerated via
  `flutter gen-l10n` on every ARB edit).
- `StudioAppState` gains `localeNotifier` alongside
  `modeNotifier`; persisted via SharedPreferences key
  `locale.code`.
- Sidebar `_LanguageToggle` reads/writes through the
  notifier. The Store's per-page locale state is gone:
  `_locale` now reads `Localizations.localeOf(context)
  .languageCode`, so the bilingual store-index content
  follows the global setting without a second toggle.
- `_NavPage.label` becomes `_NavPage.id` + `labelOf(context)`;
  Cmd+K palette and Sidebar both read the localized label.

Out of scope this iteration: localizing the remaining
~80% of UI strings (Settings dialog labels, Store search
hint, error messages). Those land incrementally — the i18n
infrastructure now means each is a one-line ARB edit + one
call-site swap.

Signed-off-by: flemming-it <stefan.a.flemming@googlemail.com>

lib/pages/store.dart

@@ -26,9 +26,15 @@ class _StorePageState extends State<StorePage> {
   String _category = '';
   String _status = '';
   bool _installedOnly = false;
-  String _locale = 'en';
   late Future<List<StoreItem>> _future;
 
+  /// Active UI locale, read from the app-wide MaterialApp
+  /// `locale` setting. Drives which side of the bilingual
+  /// store-index entries renders (taglineEn vs taglineDe,
+  /// descriptionEn vs descriptionDe). The sidebar's
+  /// language toggle flips this for the whole app.
+  String get _locale => Localizations.localeOf(context).languageCode;
+
   @override
   void initState() {
     super.initState();
@@ -97,13 +103,10 @@ class _StorePageState extends State<StorePage> {
       appBar: AppBar(
         title: const Text('Store'),
         actions: [
-          // Tiny DE/EN toggle — the store-index ships bilingual
-          // copy and operators in regulated environments often
-          // share screens with non-English colleagues.
-          _LocaleToggle(
-            value: _locale,
-            onChanged: (v) => setState(() => _locale = v),
-          ),
+          // The DE/EN toggle now lives in the sidebar footer
+          // and flips the entire app's locale. The Store
+          // detail-sheet content follows automatically because
+          // _locale reads from `Localizations.localeOf`.
           IconButton(
             icon: const Icon(Icons.refresh, size: 18),
             tooltip: 'Reload',
@@ -421,29 +424,6 @@ class _ChoiceChip extends StatelessWidget {
   }
 }
 
-class _LocaleToggle extends StatelessWidget {
-  final String value;
-  final ValueChanged<String> onChanged;
-  const _LocaleToggle({required this.value, required this.onChanged});
-
-  @override
-  Widget build(BuildContext context) {
-    return Padding(
-      padding: const EdgeInsets.only(right: FaiSpace.sm),
-      child: Tooltip(
-        message: value == 'en'
-            ? 'Showing English copy. Click to switch to German.'
-            : 'Deutsche Beschreibung — Click for English.',
-        child: TextButton.icon(
-          onPressed: () => onChanged(value == 'en' ? 'de' : 'en'),
-          icon: const Icon(Icons.translate, size: 16),
-          label: Text(value.toUpperCase()),
-        ),
-      ),
-    );
-  }
-}
-
 /// Responsive grid — wraps to as many columns as the viewport
 /// allows. Cards are click-to-expand; install is also a top-
 /// level action so single-click installs are still possible.
@@ -893,7 +873,9 @@ class _StoreDetailSheet extends StatefulWidget {
 }
 
 class _StoreDetailSheetState extends State<_StoreDetailSheet> {
-  late String _locale = widget.locale;
+  /// Locale comes from MaterialApp via `Localizations.localeOf`;
+  /// the per-sheet state from before is no longer needed.
+  String get _locale => Localizations.localeOf(context).languageCode;
   bool _busy = false;
   String? _toast;
   Future<({String errorKind, String text, String sourceUrl})>? _docsFuture;
@@ -1085,10 +1067,9 @@ class _StoreDetailSheetState extends State<_StoreDetailSheet> {
                           ],
                         ),
                       ),
-                      _LocaleToggle(
-                        value: _locale,
-                        onChanged: (v) => setState(() => _locale = v),
-                      ),
+                      // Locale follows the app-wide setting
+                      // from the sidebar; the detail sheet
+                      // does not host its own toggle anymore.
                     ],
                   ),
                   const SizedBox(height: FaiSpace.lg),