feat(shell): real sprout logo on home + basic Settings screen

- Bundle the real sprout logo (docs/logo.png → assets/logo.png) and show it on
  the home menu instead of a Material icon.
- Settings screen: switch language (Español / English / system) via slang, plus
  an About tile (logo, app name, one-line description). Drawer "Settings" is now
  active and routes to /settings.

Tests: drawer Settings opens the screen and shows the language options. 54 green.

apps/app_seeds/lib/app.dart

@@ -10,6 +10,7 @@ import 'state/inventory_cubit.dart';
 import 'state/variety_detail_cubit.dart';
 import 'ui/home_screen.dart';
 import 'ui/inventory_list_screen.dart';
+import 'ui/settings_screen.dart';
 import 'ui/theme.dart';
 import 'ui/variety_detail_screen.dart';
 
@@ -27,6 +28,10 @@ class TaneApp extends StatelessWidget {
     return GoRouter(
       routes: [
         GoRoute(path: '/', builder: (context, state) => const HomeScreen()),
+        GoRoute(
+          path: '/settings',
+          builder: (context, state) => const SettingsScreen(),
+        ),
         GoRoute(
           path: '/inventory',
           builder: (context, state) => BlocProvider(