feat(market): embed offer photos inline instead of a media server

Replace the Blossom media-server approach with a fully decentralized one:
generate a small (~320px) JPEG thumbnail from the lot's cover photo and
embed it in the offer event as a data: URI, so photos ride the relays with
no server and no IP leak. The full photo stays in the encrypted inventory.

- offer_thumbnail.dart: downscale-until-it-fits data-URI builder + decoder
- market_widgets: render data: URIs from memory, http(s) URLs from network
- offers_cubit: publish a thumbnail (best-effort) in place of an upload
- drop MediaTransport/Blossom from commons_core (http/crypto deps) and the
  media-server setting; parked on branch parked/offer-photos-blossom

Relay event-size limits cap the image to a thumbnail; higher-res sharing
would need the parked Blossom path.

apps/app_seeds/lib/i18n/strings_pt.g.dart

@@ -691,8 +691,6 @@ class _Translations$market$pt extends Translations$market$en {
 	@override String get copyId => 'Copiar código';
 	@override String get idCopied => 'Código copiado';
 	@override String get photo => 'Foto';
-	@override String get mediaServerLabel => 'Servidor de fotos';
-	@override String get mediaServerHelp => 'Onde as fotos das ofertas ficam alojadas para que outras pessoas as vejam. Deixe vazio para partilhar sem fotos.';
 }
 
 // Path: profile
@@ -1458,8 +1456,6 @@ extension on TranslationsPt {
 			'market.copyId' => 'Copiar código',
 			'market.idCopied' => 'Código copiado',
 			'market.photo' => 'Foto',
-			'market.mediaServerLabel' => 'Servidor de fotos',
-			'market.mediaServerHelp' => 'Onde as fotos das ofertas ficam alojadas para que outras pessoas as vejam. Deixe vazio para partilhar sem fotos.',
 			'profile.title' => 'O teu perfil',
 			'profile.name' => 'Nome',
 			'profile.nameHint' => 'Como os outros te veem',