feat(chat): usable 1:1 chat — bottom-anchored, Drift-backed, dated

- Anchor the message list to the bottom (`reverse: true`) so new messages
  stay in view instead of landing below the fold.
- Move chat history from the OS keystore (O(n²) JSON blob, silent 200-msg
  cap) to a separate encrypted Drift/SQLCipher DB (`ChatDatabase`):
  indexed append, uncapped history, dedup as a unique-key invariant. It's
  an ephemeral per-device cache, isolated from the inventory schema, its
  migrations, and its sync. No data migration (pre-release).
- Add day separators (Today/Yesterday/locale date) and a per-bubble time,
  all via ICU (12/24h per locale; Localizations locale maps Asturian →
  Spanish for intl date symbols).
- Add peer avatars (deterministic colour from the pubkey + name initial),
  surface send failures that were previously silent, and make bubble text
  selectable (addresses, links).
- New i18n keys in en/es/pt/ast; tests for grouping, formatting, avatars,
  scroll anchoring, storage and send errors.

Docs: docs/design/chat-storage.md + open-decisions.md.

apps/app_seeds/test/services/inbox_service_test.dart

@@ -46,7 +46,7 @@ void main() {
   late InboxService inbox;
 
   setUp(() async {
-    store = MessageStore(InMemorySecretStore());
+    store = MessageStore(newTestChatDatabase());
     inbox = InboxService(
       connection: await offlineConnection(),
       selfPubkey: 'me',

apps/app_seeds/test/services/message_store_test.dart

@@ -1,18 +1,24 @@
 import 'package:commons_core/commons_core.dart';
 import 'package:flutter_test/flutter_test.dart';
+import 'package:tane/db/chat_database.dart';
 import 'package:tane/services/message_store.dart';
 
 import '../support/test_support.dart';
 
 void main() {
+  late ChatDatabase db;
   late MessageStore store;
-  setUp(() => store = MessageStore(InMemorySecretStore()));
+  setUp(() {
+    db = newTestChatDatabase();
+    store = MessageStore(db);
+  });
+  tearDown(() => db.close());
 
-  PrivateMessage msg(String from, String text, int atMs) =>
-      PrivateMessage(
-          fromPubkey: from,
-          text: text,
-          at: DateTime.fromMillisecondsSinceEpoch(atMs));
+  PrivateMessage msg(String from, String text, int atMs) => PrivateMessage(
+    fromPubkey: from,
+    text: text,
+    at: DateTime.fromMillisecondsSinceEpoch(atMs),
+  );
 
   test('history is empty for an unknown peer', () async {
     expect(await store.history('peer'), isEmpty);
@@ -34,53 +40,62 @@ void main() {
     expect((await store.history('b')).single.text, 'toB');
   });
 
-  test('conversations lists peers newest-first with their last message',
-      () async {
-    await store.append('peerA', msg('me', 'hi A', 1000));
-    await store.append('peerB', msg('peerB', 'yo B', 3000));
-    await store.append('peerA', msg('peerA', 'back A', 2000));
+  test(
+    'conversations lists peers newest-first with their last message',
+    () async {
+      await store.append('peerA', msg('me', 'hi A', 1000));
+      await store.append('peerB', msg('peerB', 'yo B', 3000));
+      await store.append('peerA', msg('peerA', 'back A', 2000));
 
-    final convos = await store.conversations();
-    expect(convos.map((c) => c.peerPubkey), ['peerB', 'peerA']); // 3000 > 2000
-    expect(convos.first.lastText, 'yo B');
-    expect(convos.last.lastText, 'back A');
-  });
+      final convos = await store.conversations();
+      expect(convos.map((c) => c.peerPubkey), [
+        'peerB',
+        'peerA',
+      ]); // 3000 > 2000
+      expect(convos.first.lastText, 'yo B');
+      expect(convos.last.lastText, 'back A');
+    },
+  );
 
-  test('append is idempotent: a re-delivered message is not duplicated',
-      () async {
-    // Same sender + timestamp + text = the same gift wrap redelivered by a
-    // relay on resubscribe. It must not pile up.
-    expect(await store.append('peer', msg('peer', 'hola', 1000)), isTrue);
-    expect(await store.append('peer', msg('peer', 'hola', 1000)), isFalse);
-    expect(await store.history('peer'), hasLength(1));
+  test(
+    'append is idempotent: a re-delivered message is not duplicated',
+    () async {
+      // Same sender + timestamp + text = the same gift wrap redelivered by a
+      // relay on resubscribe. It must not pile up.
+      expect(await store.append('peer', msg('peer', 'hola', 1000)), isTrue);
+      expect(await store.append('peer', msg('peer', 'hola', 1000)), isFalse);
+      expect(await store.history('peer'), hasLength(1));
 
-    // A genuinely different message (later timestamp) still lands.
-    expect(await store.append('peer', msg('peer', 'hola', 2000)), isTrue);
-    expect(await store.history('peer'), hasLength(2));
-  });
+      // A genuinely different message (later timestamp) still lands.
+      expect(await store.append('peer', msg('peer', 'hola', 2000)), isTrue);
+      expect(await store.history('peer'), hasLength(2));
+    },
+  );
 
-  test('per-identity scope isolates conversations (0 = legacy keys)', () async {
-    final secret = InMemorySecretStore();
-    final acct0 = MessageStore(secret); // legacy / account 0
-    final acct1 = MessageStore(secret, accountScope: 'acct1');
+  test(
+    'per-identity scope isolates conversations (0 = legacy scope)',
+    () async {
+      final acct0 = MessageStore(db); // legacy / account 0
+      final acct1 = MessageStore(db, accountScope: 'acct1');
 
-    await acct0.append('peer', msg('peer', 'for identity 0', 1000));
-    await acct1.append('peer', msg('peer', 'for identity 1', 2000));
+      await acct0.append('peer', msg('peer', 'for identity 0', 1000));
+      await acct1.append('peer', msg('peer', 'for identity 1', 2000));
 
-    // Same peer, but each identity sees only its own conversation.
-    expect((await acct0.history('peer')).single.text, 'for identity 0');
-    expect((await acct1.history('peer')).single.text, 'for identity 1');
-    expect((await acct0.conversations()).single.lastText, 'for identity 0');
-    expect((await acct1.conversations()).single.lastText, 'for identity 1');
-  });
+      // Same peer, but each identity sees only its own conversation.
+      expect((await acct0.history('peer')).single.text, 'for identity 0');
+      expect((await acct1.history('peer')).single.text, 'for identity 1');
+      expect((await acct0.conversations()).single.lastText, 'for identity 0');
+      expect((await acct1.conversations()).single.lastText, 'for identity 1');
+    },
+  );
 
-  test('history is capped to the most recent 200', () async {
+  test('history is uncapped: nothing is silently dropped', () async {
     for (var i = 0; i < 210; i++) {
       await store.append('peer', msg('me', 'm$i', i));
     }
     final history = await store.history('peer');
-    expect(history, hasLength(200));
-    expect(history.first.text, 'm10'); // oldest 10 dropped
+    expect(history, hasLength(210));
+    expect(history.first.text, 'm0'); // the oldest survives
     expect(history.last.text, 'm209');
   });
 }

apps/app_seeds/test/services/unread_service_test.dart

@@ -15,7 +15,7 @@ void main() {
   late UnreadService unread;
 
   setUp(() {
-    store = MessageStore(InMemorySecretStore());
+    store = MessageStore(newTestChatDatabase());
     unread = UnreadService(store, InMemorySecretStore());
   });