feat(shell): home menu + navigation drawer (mockups 02/03)

The app now opens on a main menu instead of straight into the list:
- HomeScreen (mockup 02): sprout logo over a faint seed-glyph watermark, with
  big "Your inventory" (→ /inventory) and "Open market" (Block 2, "coming soon")
  destinations.
- AppDrawer (mockup 03): Inventory is live; the social items (market, profile,
  chat, wishlist, following, settings) are shown disabled with a "coming soon"
  tag so the roadmap is visible. Drawer is available on home and inventory.
- Routing: / → home, /inventory → list, /variety/:id → detail.

Tests: home shows the menu + navigates; drawer opens + navigates. quick-add flow
updated to go home → inventory. 50 green; Linux runs.

apps/app_seeds/lib/app.dart

@@ -8,13 +8,13 @@ import 'data/variety_repository.dart';
 import 'i18n/strings.g.dart';
 import 'state/inventory_cubit.dart';
 import 'state/variety_detail_cubit.dart';
+import 'ui/home_screen.dart';
 import 'ui/inventory_list_screen.dart';
 import 'ui/theme.dart';
 import 'ui/variety_detail_screen.dart';
 
-/// Root widget. Provides the repository + inventory cubit to the tree and wires
-/// go_router. The list is `/`; `/variety/:id` is a placeholder detail route
-/// (the full item screen is a follow-on story).
+/// Root widget. Provides the repositories to the tree and wires go_router:
+/// `/` is the home menu, `/inventory` the list, `/variety/:id` the item detail.
 class TaneApp extends StatelessWidget {
   TaneApp({required this.repository, required this.species, super.key})
     : _router = _buildRouter(repository);
@@ -26,8 +26,9 @@ class TaneApp extends StatelessWidget {
   static GoRouter _buildRouter(VarietyRepository repository) {
     return GoRouter(
       routes: [
+        GoRoute(path: '/', builder: (context, state) => const HomeScreen()),
         GoRoute(
-          path: '/',
+          path: '/inventory',
           builder: (context, state) => BlocProvider(
             create: (_) => InventoryCubit(repository),
             child: const InventoryListScreen(),