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/test/ui/quick_add_flow_test.dart

@@ -24,6 +24,10 @@ void main() {
       );
       await tester.pumpAndSettle();
 
+      // Home → inventory.
+      await tester.tap(find.byKey(const Key('home.inventory')));
+      await tester.pumpAndSettle();
+
       // Starts empty.
       expect(
         find.text('No seeds yet. Tap + to add your first.'),