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/lib/i18n/es.i18n.json

@@ -346,6 +346,8 @@
     "setAreaBody": "Dile al mercado tu zona aproximada para ver semillas cerca.",
     "searching": "Buscando por tu zona…",
     "empty": "Aún no hay semillas compartidas cerca de ti",
+    "searchHint": "Buscar entre estas semillas",
+    "noMatches": "Ninguna semilla compartida coincide con tu búsqueda",
     "near": "Cerca de ti",
     "contact": "Mensaje",
     "mine": "Tú",