feat(market): search + pull-to-refresh in the market list

Match the inventory patterns the market was missing:
- Search: OffersState gains a `query` + `visibleOffers` getter and
  OffersCubit.search() filters the already-discovered offers locally by
  summary (case-insensitive), never re-hitting the transport. The filter
  survives a refresh. Rounded search field mirrors inventory's.
- Pull-to-refresh: RefreshIndicator re-runs discovery for the current
  area (empty state included, so a swipe re-scans). Text filter kept.
- i18n: market.searchHint / market.noMatches (en/es/pt).

Note: the shared slang output (strings*.g.dart, incl. the generated
Asturian locale) is regenerated wholesale, so it also carries the
in-progress `ast` locale keys already present in the working tree.

apps/app_seeds/test/state/offers_cubit_test.dart

@@ -102,6 +102,56 @@ void main() {
       await cubit.close();
     });
 
+    test('search narrows visible offers by summary, keeping the full list',
+        () async {
+      final transport = FakeOfferTransport();
+      for (final s in ['Tomate rosa', 'Judía verde', 'Tomate rojo']) {
+        await transport.publish(OfferMapper.fromSharedLot(
+          lotId: s,
+          authorPubkeyHex: 'ab' * 32,
+          summary: s,
+          sharing: OfferStatus.shared,
+          areaGeohash: 'sp3e9',
+        ));
+      }
+      final cubit = OffersCubit(transport);
+      await cubit.discover('sp3');
+      await pumpEventQueue();
+      expect(cubit.state.offers, hasLength(3));
+
+      cubit.search('tomate'); // case-insensitive
+      expect(cubit.state.visibleOffers.map((o) => o.summary),
+          containsAll(['Tomate rosa', 'Tomate rojo']));
+      expect(cubit.state.visibleOffers, hasLength(2));
+      expect(cubit.state.offers, hasLength(3)); // underlying list untouched
+
+      cubit.search(''); // clearing shows everything again
+      expect(cubit.state.visibleOffers, hasLength(3));
+      await cubit.close();
+    });
+
+    test('the search filter survives a refresh (re-discovery)', () async {
+      final transport = FakeOfferTransport();
+      await transport.publish(OfferMapper.fromSharedLot(
+        lotId: 'lot-1',
+        authorPubkeyHex: 'ab' * 32,
+        summary: 'Pimiento',
+        sharing: OfferStatus.shared,
+        areaGeohash: 'sp3e9',
+      ));
+      final cubit = OffersCubit(transport);
+      await cubit.discover('sp3');
+      await pumpEventQueue();
+      cubit.search('pim');
+      expect(cubit.state.query, 'pim');
+
+      await cubit.discover('sp3'); // pull-to-refresh
+      await pumpEventQueue();
+      expect(cubit.state.query, 'pim'); // kept across the refresh
+      expect(cubit.state.visibleOffers, hasLength(1));
+      await cubit.close();
+    });
+
     test('a different area finds nothing', () async {
       final transport = FakeOfferTransport();
       await transport.publish(OfferMapper.fromSharedLot(