feat(block2): offline outbox — share now, publish when connected

Sender-side offline delivery hardening.
- OfferOutbox: a keystore-backed (no plaintext) queue of lot ids to publish
  later. Stores ids, not offers, so on flush each offer is rebuilt from the
  lot's CURRENT state — an offline edit is respected, a deleted lot drops out.
- flushOutbox(): on reconnect, republishes queued lots and clears them (no-op
  offline; drops ids whose lot is gone).
- Market screen: sharing offline parks the lots ('we'll share these when you're
  connected'); opening the market online auto-flushes the queue first.
- Wired via DI + TaneApp(outbox); i18n en/es/pt.

Tests: 4 outbox + 3 flush + market UI, 20 green. Analyzer clean for new code.

apps/app_seeds/lib/app.dart

@@ -8,6 +8,7 @@ import 'data/species_repository.dart';
 import 'data/variety_repository.dart';
 import 'i18n/strings.g.dart';
 import 'services/coarse_location.dart';
+import 'services/offer_outbox.dart';
 import 'services/onboarding_store.dart';
 import 'services/social_service.dart';
 import 'services/social_settings.dart';
@@ -33,6 +34,7 @@ class TaneApp extends StatelessWidget {
     this.social,
     this.socialSettings,
     this.location,
+    this.outbox,
     this.showIntro = false,
     super.key,
   }) : _router = _buildRouter(
@@ -42,6 +44,7 @@ class TaneApp extends StatelessWidget {
           social,
           socialSettings,
           location,
+          outbox,
         );
 
   final VarietyRepository repository;
@@ -55,6 +58,9 @@ class TaneApp extends StatelessWidget {
 
   /// Optional device-location source for the market's "use my location".
   final CoarseLocationProvider? location;
+
+  /// Optional offline outbox for the market's "share my seeds".
+  final OfferOutbox? outbox;
   final bool showIntro;
   final GoRouter _router;
 
@@ -65,6 +71,7 @@ class TaneApp extends StatelessWidget {
     SocialService? social,
     SocialSettings? socialSettings,
     CoarseLocationProvider? location,
+    OfferOutbox? outbox,
   ) {
     return GoRouter(
       initialLocation: showIntro ? '/intro' : '/',
@@ -81,6 +88,7 @@ class TaneApp extends StatelessWidget {
               social: social,
               settings: socialSettings,
               location: location,
+              outbox: outbox,
             ),
           ),
         GoRoute(