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/test/state/peer_rating_cubit_test.dart

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+import 'package:commons_core/commons_core.dart';
+import 'package:flutter_test/flutter_test.dart';
+import 'package:tane/state/peer_rating_cubit.dart';
+
+/// In-memory [RatingTransport]: rate/retract act as this device's identity,
+/// one live rating per (rater, subject) like the Nostr transport.
+class FakeRatingTransport implements RatingTransport {
+  FakeRatingTransport(this.selfId);
+  final String selfId;
+  final Map<String, Map<String, Rating>> _bySubject = {}; // subject -> rater
+
+  /// Test helper: record an arbitrary rater→subject rating.
+  void addRating(String rater, String subject, int stars,
+          {String comment = ''}) =>
+      (_bySubject[subject] ??= {})[rater] = Rating(
+        rater: rater,
+        subject: subject,
+        stars: stars,
+        ratedAt: DateTime(2026),
+        comment: comment,
+      );
+
+  @override
+  Future<void> rate({
+    required String subjectPubkey,
+    required int stars,
+    String comment = '',
+  }) async =>
+      addRating(selfId, subjectPubkey, stars, comment: comment);
+
+  @override
+  Future<void> retract({required String subjectPubkey}) async =>
+      _bySubject[subjectPubkey]?.remove(selfId);
+
+  @override
+  Future<List<Rating>> ratingsOf(String subjectPubkey) async =>
+      List.of(_bySubject[subjectPubkey]?.values ?? const <Rating>[]);
+
+  @override
+  Future<Rating?> myRatingOf(String subjectPubkey) async =>
+      _bySubject[subjectPubkey]?[selfId];
+
+  @override
+  Future<void> close() async {}
+}
+
+/// Minimal trust transport exposing a fixed certification graph, for the
+/// circle weighting.
+class FakeTrustTransport implements TrustTransport {
+  final List<Certification> certs = [];
+
+  void addCert(String issuer, String subject) => certs.add(Certification(
+        issuer: issuer,
+        subject: subject,
+        issuedAt: DateTime(2026),
+      ));
+
+  @override
+  Future<List<Certification>> allCertifications() async => List.of(certs);
+
+  @override
+  Future<Set<String>> certifiersOf(String subjectPubkey) async => {
+        for (final c in certs)
+          if (c.subject == subjectPubkey) c.issuer,
+      };
+
+  @override
+  Future<void> certify({
+    required String subjectPubkey,
+    Duration validity = const Duration(days: 365),
+    String note = '',
+  }) async {}
+
+  @override
+  Future<void> revoke({required String subjectPubkey}) async {}
+
+  @override
+  Future<void> close() async {}
+}
+
+void main() {
+  const me = 'me';
+  const peer = 'peer';
+
+  test('aggregates count and average over active ratings', () async {
+    final ratings = FakeRatingTransport(me)
+      ..addRating('a', peer, 5)
+      ..addRating('b', peer, 2);
+    final cubit = PeerRatingCubit(ratings, peerPubkey: peer, selfPubkey: me);
+    await cubit.load();
+    expect(cubit.state.count, 2);
+    expect(cubit.state.average, closeTo(3.5, 0.001));
+    expect(cubit.state.circleCount, 0); // no trust graph wired
+    expect(cubit.state.iRated, isFalse);
+    await cubit.close();
+  });
+
+  test('counts ratings coming from your circle', () async {
+    final ratings = FakeRatingTransport(me)
+      ..addRating('friend', peer, 5) // you vouch for 'friend'
+      ..addRating('stranger', peer, 1);
+    final trust = FakeTrustTransport()..addCert(me, 'friend');
+    final cubit = PeerRatingCubit(
+      ratings,
+      peerPubkey: peer,
+      selfPubkey: me,
+      trust: trust,
+    );
+    await cubit.load();
+    expect(cubit.state.count, 2);
+    expect(cubit.state.circleCount, 1);
+    await cubit.close();
+  });
+
+  test('rate publishes then reloads; re-rating replaces', () async {
+    final ratings = FakeRatingTransport(me);
+    final cubit = PeerRatingCubit(ratings, peerPubkey: peer, selfPubkey: me);
+    await cubit.load();
+
+    await cubit.rate(4, comment: 'Nice seeds');
+    expect(cubit.state.myStars, 4);
+    expect(cubit.state.myComment, 'Nice seeds');
+    expect(cubit.state.count, 1);
+
+    await cubit.rate(2);
+    expect(cubit.state.myStars, 2);
+    expect(cubit.state.count, 1); // replaced, not piled up
+    await cubit.close();
+  });
+
+  test('retract removes your rating', () async {
+    final ratings = FakeRatingTransport(me)..addRating(me, peer, 3);
+    final cubit = PeerRatingCubit(ratings, peerPubkey: peer, selfPubkey: me);
+    await cubit.load();
+    expect(cubit.state.iRated, isTrue);
+
+    await cubit.retract();
+    expect(cubit.state.iRated, isFalse);
+    expect(cubit.state.count, 0);
+    await cubit.close();
+  });
+
+  test('never rates self', () async {
+    final ratings = FakeRatingTransport(me);
+    final cubit = PeerRatingCubit(ratings, peerPubkey: me, selfPubkey: me);
+    await cubit.load();
+    await cubit.rate(5);
+    expect(cubit.state.iRated, isFalse);
+    expect(cubit.state.count, 0);
+    await cubit.close();
+  });
+
+  test('offline (no transport) never throws', () async {
+    final cubit = PeerRatingCubit(null, peerPubkey: peer, selfPubkey: me);
+    expect(cubit.isOnline, isFalse);
+    await cubit.load();
+    await cubit.rate(5);
+    await cubit.retract();
+    expect(cubit.state.loading, isFalse);
+    await cubit.close();
+  });
+}