feat(profile): profile photo or seed-illustration avatar

Profiles had only a coloured-initial disc. Now each person can set an
avatar — a real photo OR one of our own seed illustrations (so
pseudonymity stays the default; no photo required).

- ui/avatar.dart: the one-string value scheme carried in the kind:0
  'picture' — a 'data:' photo thumbnail, a 'tane:seed:<glyph>' token, or
  empty. The Nostr ProfileTransport already published 'picture'.
- Photos ride inline as a tiny thumbnail (reuses offerThumbnailDataUri,
  24 KB cap) — no media server, like offer photos.
- avatar_edit.dart: pick/take a photo, choose a seed illustration, or
  remove; ProfileStore stores it; ProfileScreen shows a big editable
  avatar and publishes it.
- PeerAvatar renders photo / illustration / initial fallback.
- ProfileCache gains picture/setPicture; the inbox caches peers' avatars
  alongside their names.
- i18n avatar block (en/es/pt/ast). Tests: value scheme + PeerAvatar
  render modes, store + cache round-trips.

Follow-up: render peers' avatars in chat/market/your-people (thread the
cached picture into PeerAvatar at each call site).

apps/app_seeds/lib/ui/profile_screen.dart

@@ -9,6 +9,8 @@ import '../services/social_account_store.dart';
 import '../services/profile_store.dart';
 import '../services/social_connection.dart';
 import '../services/social_service.dart';
+import 'avatar_edit.dart';
+import 'peer_avatar.dart';
 import 'qr_view.dart';
 import 'restart_widget.dart';
 import 'theme.dart';
@@ -44,6 +46,7 @@ class _ProfileScreenState extends State<ProfileScreen> {
   final _name = TextEditingController();
   final _about = TextEditingController();
   final _g1 = TextEditingController();
+  String _avatar = '';
   bool _loading = true;
   bool _saving = false;
   bool _switching = false;
@@ -62,6 +65,7 @@ class _ProfileScreenState extends State<ProfileScreen> {
     _name.text = await widget.profileStore.name();
     _about.text = await widget.profileStore.about();
     _g1.text = await widget.profileStore.g1();
+    _avatar = await widget.profileStore.avatar();
     final max = await widget.accounts.maxCreated();
     final ids = <({int account, String npub})>[];
     for (var i = 0; i <= max; i++) {
@@ -108,6 +112,11 @@ class _ProfileScreenState extends State<ProfileScreen> {
     await _switchTo(next, confirm: false); // creating one is already explicit
   }
 
+  Future<void> _editAvatar() async {
+    final result = await showAvatarPicker(context, current: _avatar);
+    if (result != null && mounted) setState(() => _avatar = result);
+  }
+
   Future<void> _copyId() async {
     final messenger = ScaffoldMessenger.of(context);
     final t = context.t;
@@ -120,8 +129,8 @@ class _ProfileScreenState extends State<ProfileScreen> {
     final messenger = ScaffoldMessenger.of(context);
     final t = context.t;
     setState(() => _saving = true);
-    await widget.profileStore
-        .save(name: _name.text, about: _about.text, g1: _g1.text);
+    await widget.profileStore.save(
+        name: _name.text, about: _about.text, g1: _g1.text, avatar: _avatar);
 
     // Best-effort publish over the shared connection so peers see the name.
     try {
@@ -129,6 +138,7 @@ class _ProfileScreenState extends State<ProfileScreen> {
       await session?.profile.publish(
         name: _name.text.trim(),
         about: _about.text.trim(),
+        picture: _avatar,
         g1: _g1.text.trim(),
       );
     } catch (_) {
@@ -157,6 +167,33 @@ class _ProfileScreenState extends State<ProfileScreen> {
           : ListView(
               padding: const EdgeInsets.all(20),
               children: [
+                Center(
+                  child: GestureDetector(
+                    key: const Key('profile.avatar'),
+                    onTap: _editAvatar,
+                    child: Stack(
+                      alignment: AlignmentDirectional.bottomEnd,
+                      children: [
+                        PeerAvatar(
+                          pubkey: widget.social.publicKeyHex,
+                          name: _name.text,
+                          picture: _avatar,
+                          radius: 44,
+                        ),
+                        Container(
+                          padding: const EdgeInsets.all(5),
+                          decoration: const BoxDecoration(
+                            color: seedGreen,
+                            shape: BoxShape.circle,
+                          ),
+                          child: const Icon(Icons.edit,
+                              size: 15, color: Colors.white),
+                        ),
+                      ],
+                    ),
+                  ),
+                ),
+                const SizedBox(height: 20),
                 _IdentityCard(npub: widget.social.npub, onCopy: _copyId),
                 const SizedBox(height: 24),
                 TextField(