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/services/offer_thumbnail.dart

@@ -0,0 +1,56 @@
+import 'dart:convert';
+import 'dart:typed_data';
+
+import 'package:image/image.dart' as img;
+
+/// Builds a tiny `data:image/jpeg;base64,…` thumbnail from a full photo, small
+/// enough to ride *inside* a Nostr offer event — no media server, fully
+/// decentralized. The full-resolution photo stays in the encrypted local
+/// inventory; only this shrunken preview is published so peers can see the seed.
+///
+/// Relays cap event size, so we downscale (longest edge) and re-encode until the
+/// base64 fits under [maxBytes]. Returns null when the bytes aren't a decodable
+/// image or no size small enough is reachable — the offer then publishes without
+/// a photo (graceful, never a hard failure).
+String? offerThumbnailDataUri(
+  Uint8List bytes, {
+  int maxBytes = 40000,
+  List<int> edges = const [320, 256, 192, 128],
+  int quality = 68,
+}) {
+  try {
+    final decoded = img.decodeImage(bytes);
+    if (decoded == null) return null;
+
+    for (final edge in edges) {
+      final resized = _fitWithin(decoded, edge);
+      final jpeg = img.encodeJpg(resized, quality: quality);
+      final b64 = base64.encode(jpeg);
+      if (b64.length <= maxBytes) return 'data:image/jpeg;base64,$b64';
+    }
+    return null; // even the smallest edge didn't fit — skip the image
+  } catch (_) {
+    return null; // undecodable/corrupt bytes — publish without a photo
+  }
+}
+
+/// Extracts the raw bytes from a `data:...;base64,…` URI, or null when [uri] is
+/// not a base64 data URI. Used by the UI to render an inline thumbnail with
+/// `Image.memory` instead of a network fetch.
+Uint8List? decodeDataUri(String uri) {
+  if (!uri.startsWith('data:')) return null;
+  try {
+    return Uri.parse(uri).data?.contentAsBytes();
+  } on FormatException {
+    return null;
+  }
+}
+
+/// Resizes [image] so its longest edge is at most [edge], preserving aspect
+/// ratio. Never upscales a photo that's already smaller.
+img.Image _fitWithin(img.Image image, int edge) {
+  if (image.width <= edge && image.height <= edge) return image;
+  return image.width >= image.height
+      ? img.copyResize(image, width: edge)
+      : img.copyResize(image, height: edge);
+}

apps/app_seeds/lib/services/social_service.dart

@@ -39,34 +39,20 @@ class SocialService {
   /// Opens a session against [relayUrls]: one fault-tolerant pool carrying all
   /// three transports (offers, messaging, trust). Relays that are down are
   /// skipped; throws only when none are reachable. Caller closes it.
-  ///
-  /// [mediaServerUrl] (a Blossom endpoint) enables offer photos: when set, the
-  /// session exposes a [MediaTransport] to host images. It rides HTTP, not the
-  /// relay pool, so it's independent of relay reachability.
-  Future<SocialSession> openSession(
-    List<String> relayUrls, {
-    String? mediaServerUrl,
-  }) async {
+  Future<SocialSession> openSession(List<String> relayUrls) async {
     final pool = await RelayPool.connect(relayUrls, identity: identity);
-    return SocialSession(pool, mediaServerUrl: mediaServerUrl);
+    return SocialSession(pool);
   }
 }
 
 /// One relay channel with the three transports on top — the
-/// "one channel, three interfaces" shape, at the app layer. Media rides its own
-/// HTTP endpoint (Blossom), so it's a fourth transport but not on the channel.
+/// "one channel, three interfaces" shape, at the app layer.
 class SocialSession {
-  SocialSession(this._channel, {String? mediaServerUrl})
+  SocialSession(this._channel)
       : offers = NostrOfferTransport(_channel),
         messages = NostrMessageTransport(_channel),
         trust = NostrTrustTransport(_channel),
-        profile = NostrProfileTransport(_channel),
-        media = (mediaServerUrl != null && mediaServerUrl.trim().isNotEmpty)
-            ? BlossomMediaTransport(
-                Uri.parse(mediaServerUrl.trim()),
-                _channel.privateKeyHex,
-              )
-            : null;
+        profile = NostrProfileTransport(_channel);
 
   final NostrChannel _channel;
 
@@ -75,14 +61,7 @@ class SocialSession {
   final TrustTransport trust;
   final ProfileTransport profile;
 
-  /// Hosts offer photos, or null when no media server is configured (offers then
-  /// publish without images).
-  final MediaTransport? media;
-
-  Future<void> close() async {
-    await media?.close();
-    await _channel.close();
-  }
+  Future<void> close() => _channel.close();
 }
 
 Uint8List _hexToBytes(String hex) {

apps/app_seeds/lib/services/social_settings.dart

@@ -17,7 +17,6 @@ class SocialSettings {
   static const _areaKey = 'tane.social.area_geohash';
   static const _relaysKey = 'tane.social.relays';
   static const _searchPrecisionKey = 'tane.social.search_precision';
-  static const _mediaServerKey = 'tane.social.media_server';
 
   /// How wide "your zone" searches, as a geohash prefix length: 5 ≈ ±2.4 km
   /// ("very close"), 4 ≈ ±20 km ("around here"), 3 ≈ ±78 km ("my region").
@@ -40,11 +39,6 @@ class SocialSettings {
     'wss://relay.primal.net',
   ];
 
-  /// Blossom media server used to host offer photos so peers can see them. The
-  /// Comunes-run server is the non-commercial default; the user can point this
-  /// at any Blossom server, or clear it to publish offers without photos.
-  static const String defaultMediaServer = 'https://blossom.comunes.org';
-
   /// The user's coarse area as a low-precision geohash (may be empty). Set
   /// manually or from device location; the transport coarsens it further.
   Future<String> areaGeohash() async => (await _store.read(_areaKey)) ?? '';
@@ -79,18 +73,6 @@ class SocialSettings {
   Future<void> setSearchPrecision(int precision) =>
       _store.write(_searchPrecisionKey, '${_clampPrecision(precision)}');
 
-  /// The Blossom media server for offer photos. Falls back to
-  /// [defaultMediaServer] until the user configures one; an explicitly saved
-  /// empty value turns photo hosting off (offers still publish, without images).
-  Future<String> mediaServerUrl() async {
-    final raw = await _store.read(_mediaServerKey);
-    if (raw == null) return defaultMediaServer; // never configured
-    return raw.trim();
-  }
-
-  Future<void> setMediaServerUrl(String url) =>
-      _store.write(_mediaServerKey, url.trim());
-
   int _clampPrecision(int p) => p < minSearchPrecision
       ? minSearchPrecision
       : (p > maxSearchPrecision ? maxSearchPrecision : p);