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/ui/rating_sheet_test.dart

@@ -0,0 +1,124 @@
+import 'package:commons_core/commons_core.dart';
+import 'package:flutter/material.dart';
+import 'package:flutter_localizations/flutter_localizations.dart';
+import 'package:flutter_test/flutter_test.dart';
+import 'package:tane/i18n/strings.g.dart';
+import 'package:tane/state/peer_rating_cubit.dart';
+import 'package:tane/ui/rating_sheet.dart';
+
+/// In-memory [RatingTransport] (one live rating per pair).
+class FakeRatingTransport implements RatingTransport {
+  FakeRatingTransport(this.selfId);
+  final String selfId;
+  final Map<String, Rating> byRater = {};
+
+  @override
+  Future<void> rate({
+    required String subjectPubkey,
+    required int stars,
+    String comment = '',
+  }) async =>
+      byRater[selfId] = Rating(
+        rater: selfId,
+        subject: subjectPubkey,
+        stars: stars,
+        ratedAt: DateTime(2026),
+        comment: comment,
+      );
+
+  @override
+  Future<void> retract({required String subjectPubkey}) async =>
+      byRater.remove(selfId);
+
+  @override
+  Future<List<Rating>> ratingsOf(String subjectPubkey) async =>
+      List.of(byRater.values);
+
+  @override
+  Future<Rating?> myRatingOf(String subjectPubkey) async => byRater[selfId];
+
+  @override
+  Future<void> close() async {}
+}
+
+void main() {
+  const me = 'me';
+  const peer = 'peer';
+
+  late FakeRatingTransport transport;
+  late PeerRatingCubit cubit;
+
+  setUp(() async {
+    LocaleSettings.setLocaleSync(AppLocale.en);
+    transport = FakeRatingTransport(me);
+    cubit = PeerRatingCubit(transport, peerPubkey: peer, selfPubkey: me);
+    await cubit.load();
+  });
+
+  tearDown(() => cubit.close());
+
+  Widget host() => TranslationProvider(
+        child: MaterialApp(
+          locale: AppLocale.en.flutterLocale,
+          supportedLocales: AppLocaleUtils.supportedLocales,
+          localizationsDelegates: const [
+            GlobalMaterialLocalizations.delegate,
+            GlobalWidgetsLocalizations.delegate,
+            GlobalCupertinoLocalizations.delegate,
+          ],
+          home: Scaffold(
+            body: Builder(
+              builder: (context) => Center(
+                child: TextButton(
+                  onPressed: () => showRatingSheet(context, cubit),
+                  child: const Text('open'),
+                ),
+              ),
+            ),
+          ),
+        ),
+      );
+
+  testWidgets('picking stars and saving publishes the rating',
+      (tester) async {
+    await tester.pumpWidget(host());
+    await tester.tap(find.text('open'));
+    await tester.pumpAndSettle();
+
+    expect(find.text('Rate this person'), findsOneWidget);
+    // Save is disabled until stars are picked.
+    expect(
+      tester.widget<FilledButton>(find.byKey(const Key('rating.save'))).enabled,
+      isFalse,
+    );
+
+    await tester.tap(find.byKey(const Key('rating.star.4')));
+    await tester.pump();
+    await tester.enterText(
+        find.byKey(const Key('rating.comment')), 'Great swap');
+    await tester.tap(find.byKey(const Key('rating.save')));
+    await tester.pumpAndSettle();
+
+    final mine = transport.byRater[me]!;
+    expect(mine.stars, 4);
+    expect(mine.comment, 'Great swap');
+    expect(find.text('Rating saved'), findsOneWidget); // snackbar
+  });
+
+  testWidgets('opens pre-filled when you already rated; retract removes',
+      (tester) async {
+    await cubit.rate(3, comment: 'Fine');
+
+    await tester.pumpWidget(host());
+    await tester.tap(find.text('open'));
+    await tester.pumpAndSettle();
+
+    expect(find.text('Edit your rating'), findsOneWidget);
+    expect(find.text('Fine'), findsOneWidget); // comment pre-filled
+
+    await tester.tap(find.byKey(const Key('rating.retract')));
+    await tester.pumpAndSettle();
+
+    expect(transport.byRater, isEmpty);
+  });
+}