feat(block2): market screen — discover seeds near you (offers UI)

Wires the 'coming soon' market card to a real discovery screen (mockups 04/05):
- MarketScreen: opens an OfferTransport lazily; local-first, so it degrades to a
  human 'set up sharing' prompt when no relay/area is set or the net is down.
- Discovers offers by the saved coarse area, lists them with human reciprocity
  labels (gift/swap/for sale), 'near you' (never exact location), price only for
  sales. Config sheet to set area + community servers (no bundled public relays).
- Threaded via TaneApp(social, socialSettings) — null keeps the card 'coming
  soon' (so Block 1 tests pass unchanged); main wires it live.
- i18n en/es/pt (market.*), reuses share.* for type labels.

3 market widget tests + home tests green; app_seeds analyzes clean.

apps/app_seeds/lib/main.dart

@@ -6,6 +6,8 @@ import 'data/variety_repository.dart';
 import 'di/injector.dart';
 import 'i18n/strings.g.dart';
 import 'services/onboarding_store.dart';
+import 'services/social_service.dart';
+import 'services/social_settings.dart';
 
 Future<void> main() async {
   WidgetsFlutterBinding.ensureInitialized();
@@ -18,6 +20,8 @@ Future<void> main() async {
         repository: getIt<VarietyRepository>(),
         species: getIt<SpeciesRepository>(),
         onboarding: onboarding,
+        social: getIt<SocialService>(),
+        socialSettings: getIt<SocialSettings>(),
         showIntro: !await onboarding.introSeen(),
       ),
     ),