feat(block2): publish my seeds to the network (completes publish->discover)

The other half of the market: share your marked lots as offers.
- VarietyRepository.shareableLots(): non-private lots WITH their id (stable,
  updatable offer id) + the variety label. Private lots never leave the device.
- OffersCubit.publishLots(): maps each via OfferMapper and publishes, tagged
  with the coarse area + signed by the derived key; counts acceptances; no-op
  offline or with no area.
- Market screen: a 'share my seeds' action (online only) — publishes, then
  re-discovers to show them; 'mark some seeds first' when nothing's shared.
- i18n en/es/pt.

14 tests green (repo query, cubit publish, market UI); analyzer clean for new code.

apps/app_seeds/lib/ui/market_screen.dart

@@ -2,6 +2,7 @@ import 'package:commons_core/commons_core.dart';
 import 'package:flutter/material.dart';
 import 'package:flutter_bloc/flutter_bloc.dart';
 
+import '../data/variety_repository.dart';
 import '../i18n/strings.g.dart';
 import '../services/social_service.dart';
 import '../services/social_settings.dart';
@@ -57,6 +58,36 @@ class _MarketScreenState extends State<MarketScreen> {
     if (changed == true) await _init();
   }
 
+  /// Publishes the user's shared lots as offers to the network, tagged with the
+  /// coarse area. Prompts for setup when the area isn't set.
+  Future<void> _shareMine() async {
+    final cubit = _cubit;
+    if (cubit == null || !cubit.isOnline) return;
+    final repo = context.read<VarietyRepository>();
+    final messenger = ScaffoldMessenger.of(context);
+    final t = context.t;
+    final area = await widget.settings.areaGeohash();
+    if (!mounted) return;
+    if (area.isEmpty) {
+      await _openConfig();
+      return;
+    }
+    final lots = await repo.shareableLots();
+    if (!mounted) return;
+    if (lots.isEmpty) {
+      messenger.showSnackBar(SnackBar(content: Text(t.market.nothingToShare)));
+      return;
+    }
+    final count = await cubit.publishLots(
+      lots,
+      authorPubkeyHex: widget.social.publicKeyHex,
+      areaGeohash: area,
+    );
+    if (!mounted) return;
+    messenger.showSnackBar(SnackBar(content: Text(t.market.sharedCount(n: count))));
+    await cubit.discover(area); // refresh — now including the just-shared lots
+  }
+
   @override
   void dispose() {
     _cubit?.close();
@@ -71,6 +102,13 @@ class _MarketScreenState extends State<MarketScreen> {
       appBar: AppBar(
         title: Text(t.market.title),
         actions: [
+          if (cubit != null && cubit.isOnline)
+            IconButton(
+              key: const Key('market.shareMine'),
+              icon: const Icon(Icons.ios_share_outlined),
+              tooltip: t.market.shareMine,
+              onPressed: _shareMine,
+            ),
           IconButton(
             key: const Key('market.config'),
             icon: const Icon(Icons.tune),