feat(ratings): Wallapop-style ratings in chat and offer detail

- SocialSession grows a ratings transport (fifth interface on the one
  shared channel).
- PeerRatingCubit: count, locale-aware average, and circleCount — how
  many ratings come from your own circle (reuses the ego-centric trust
  rule), the signal that makes strangers' review-stuffing irrelevant.
- Chat: slim rating strip under the trust banner; you can rate only
  someone you've talked with (soft anchor until the signed bilateral
  exchange form lands). Sheet with 5 stars + optional comment,
  pre-filled for editing, with a take-back action.
- Offer detail: author's stars under their name, with 'N from people
  you know' when your circle rated them; nothing shown when unrated.
- i18n ratings.* (en/es/pt/ast); tests for cubit and sheet.

apps/app_seeds/lib/services/social_service.dart

@@ -89,13 +89,14 @@ class SocialService {
   }
 }
 
-/// One relay channel with the three transports on top — the
-/// "one channel, three interfaces" shape, at the app layer.
+/// One relay channel with the transports on top — the
+/// "one channel, N interfaces" shape, at the app layer.
 class SocialSession {
   SocialSession(this._channel, {String deviceId = ''})
       : offers = NostrOfferTransport(_channel),
         messages = NostrMessageTransport(_channel),
         trust = NostrTrustTransport(_channel),
+        ratings = NostrRatingTransport(_channel),
         profile = NostrProfileTransport(_channel),
         sync = NostrSyncTransport(
           _channel,
@@ -108,6 +109,7 @@ class SocialSession {
   final OfferTransport offers;
   final MessageTransport messages;
   final TrustTransport trust;
+  final RatingTransport ratings;
   final ProfileTransport profile;
 
   /// Device-to-device inventory sync for THIS identity's own devices.