feat(market): fix publish-duplicates, add offer detail page + filters

The vecino/market view had three gaps:

- Publishing inventory duplicated the listing. discover() appended every
  offer the relay streamed, but relays legitimately resend an addressable
  NIP-99 event (stored copy + live echo on publish). Merge by
  (authorPubkeyHex, id) so each offer appears once; two authors reusing a
  lot id stay distinct.
- No product detail. Tapping a card jumped straight to chat. Add a
  read-only "product page" (MarketOfferDetailScreen) with title, mode,
  category, eco badge, coarse location, price, a "Shared by" seller
  section (profile fetched by pubkey) and the message button. Reached via
  a new /market/offer route; cards are now fully tappable. Shows only what
  the network already carries — no photos/description added to the wire.
- No filters. Add a filter bar (type, category, eco) mirroring inventory,
  each chip group shown only when a discovered offer can match it. To make
  the eco filter real, publish the organic flag on the wire: Offer.isOrganic
  -> NIP-99 'organic' tag -> OfferMapper -> ShareableLot.

Tests: commons_core organic round-trip; app-side dedup, two-author
separation, filter logic, mapper passthrough; detail-screen widget tests.
i18n keys added to en/es/pt/ast and slang regenerated.

packages/commons_core/lib/src/social/nostr/nip99_codec.dart

@@ -30,6 +30,7 @@ class Nip99Codec {
       tags.add(['g', coarse.substring(0, i)]); // NIP-52 prefix ladder, coarse only
     }
     if (offer.category != null) tags.add(['t', offer.category!]);
+    if (offer.isOrganic) tags.add(['organic', '1']);
     if (offer.radiusKm != null) tags.add(['radius_km', '${offer.radiusKm}']);
     if (offer.type == OfferType.sale && offer.priceAmount != null) {
       tags.add(['price', '${offer.priceAmount}', offer.priceCurrency ?? 'EUR']);
@@ -62,6 +63,7 @@ class Nip99Codec {
       priceCurrency: price != null && price.length > 2 ? price[2] : null,
       exchangeTerms: _tagValue(event, 'exchange_terms'),
       imageUrl: _tagValue(event, 'image'),
+      isOrganic: _tagValue(event, 'organic') == '1',
     );
   }
 

packages/commons_core/lib/src/social/offer.dart

@@ -29,6 +29,7 @@ class Offer {
     this.radiusKm,
     this.imageUrl,
     this.expiresAt,
+    this.isOrganic = false,
   });
 
   /// Stable per-offer identifier (NIP-99 `d` tag → addressable event).
@@ -57,6 +58,10 @@ class Offer {
 
   final String? imageUrl;
   final DateTime? expiresAt;
+
+  /// Grower-declared organic ("eco") provenance — a self-declaration the author
+  /// chose to publish, so peers can filter for it. Never a certification.
+  final bool isOrganic;
 }
 
 /// Result of publishing to a transport.