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/app.dart

@@ -8,12 +8,15 @@ import 'data/species_repository.dart';
 import 'data/variety_repository.dart';
 import 'i18n/strings.g.dart';
 import 'services/onboarding_store.dart';
+import 'services/social_service.dart';
+import 'services/social_settings.dart';
 import 'state/inventory_cubit.dart';
 import 'state/variety_detail_cubit.dart';
 import 'ui/about_screen.dart';
 import 'ui/home_screen.dart';
 import 'ui/intro_screen.dart';
 import 'ui/inventory_list_screen.dart';
+import 'ui/market_screen.dart';
 import 'ui/settings_screen.dart';
 import 'ui/theme.dart';
 import 'ui/variety_detail_screen.dart';
@@ -26,13 +29,26 @@ class TaneApp extends StatelessWidget {
     required this.repository,
     required this.species,
     required this.onboarding,
+    this.social,
+    this.socialSettings,
     this.showIntro = false,
     super.key,
-  }) : _router = _buildRouter(repository, onboarding, showIntro);
+  }) : _router = _buildRouter(
+          repository,
+          onboarding,
+          showIntro,
+          social,
+          socialSettings,
+        );
 
   final VarietyRepository repository;
   final SpeciesRepository species;
   final OnboardingStore onboarding;
+
+  /// Block 2 social layer. Null until the social round is wired in `main`; when
+  /// null the market stays a "coming soon" card and `/market` is not routed.
+  final SocialService? social;
+  final SocialSettings? socialSettings;
   final bool showIntro;
   final GoRouter _router;
 
@@ -40,11 +56,23 @@ class TaneApp extends StatelessWidget {
     VarietyRepository repository,
     OnboardingStore onboarding,
     bool showIntro,
+    SocialService? social,
+    SocialSettings? socialSettings,
   ) {
     return GoRouter(
       initialLocation: showIntro ? '/intro' : '/',
       routes: [
-        GoRoute(path: '/', builder: (context, state) => const HomeScreen()),
+        GoRoute(
+          path: '/',
+          builder: (context, state) =>
+              HomeScreen(marketEnabled: social != null),
+        ),
+        if (social != null && socialSettings != null)
+          GoRoute(
+            path: '/market',
+            builder: (context, state) =>
+                MarketScreen(social: social, settings: socialSettings),
+          ),
         GoRoute(
           path: '/intro',
           builder: (context, state) => IntroScreen(