feat(market): show offer photos in the market list and detail

Render offer.imageUrl (already carried by NIP-99) as a thumbnail on each
market card and a hero image on the offer detail page. Remote images
degrade gracefully: a spinner while loading, a neutral placeholder when
the media server is unreachable. Publishing the photo comes next.

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

@@ -1282,6 +1282,9 @@ class Translations$market$en {
 
 	/// en: 'Code copied'
 	String get idCopied => 'Code copied';
+
+	/// en: 'Photo'
+	String get photo => 'Photo';
 }
 
 // Path: profile
@@ -2220,6 +2223,7 @@ extension on Translations {
 			'market.noProfile' => 'This person hasn\'t shared a profile yet',
 			'market.copyId' => 'Copy code',
 			'market.idCopied' => 'Code copied',
+			'market.photo' => 'Photo',
 			'profile.title' => 'Your profile',
 			'profile.name' => 'Display name',
 			'profile.nameHint' => 'How others see you',