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/peer_avatar.dart

@@ -1,23 +1,50 @@
 import 'package:flutter/material.dart';
 
-/// A small round avatar for a chat peer. We have no profile photos yet, so it's
-/// a deterministic disc coloured from the peer's pubkey, showing the first
-/// letter of their [name] when known (else a person glyph). Same pubkey → same
-/// colour on every device, so the peer is visually recognizable.
+import '../services/offer_thumbnail.dart' show decodeDataUri;
+import 'avatar.dart';
+import 'seed_glyph.dart';
+
+/// A small round avatar for a person. When they've set an avatar ([picture] — a
+/// `data:` photo thumbnail or a `tane:seed:<glyph>` illustration) it's shown;
+/// otherwise it falls back to a deterministic disc coloured from their [pubkey],
+/// with the first letter of their [name] (else a person glyph). Same pubkey →
+/// same colour on every device, so a person stays visually recognizable.
 class PeerAvatar extends StatelessWidget {
   const PeerAvatar({
     required this.pubkey,
     this.name,
+    this.picture,
     this.radius = 14,
     super.key,
   });
 
   final String pubkey;
   final String? name;
+
+  /// The person's chosen avatar value; null/empty → the coloured-initial disc.
+  final String? picture;
   final double radius;
 
   @override
   Widget build(BuildContext context) {
+    final pic = picture?.trim() ?? '';
+
+    if (pic.startsWith('data:')) {
+      final bytes = decodeDataUri(pic);
+      if (bytes != null) {
+        return CircleAvatar(radius: radius, backgroundImage: MemoryImage(bytes));
+      }
+    } else if (pic.startsWith(avatarGlyphPrefix)) {
+      final glyph = avatarGlyphChar(pic.substring(avatarGlyphPrefix.length));
+      if (glyph != null) {
+        return CircleAvatar(
+          radius: radius,
+          backgroundColor: peerAvatarColor(pubkey),
+          child: SeedGlyph(glyph, size: radius * 1.15, color: Colors.white),
+        );
+      }
+    }
+
     final letter = _initial(name);
     return CircleAvatar(
       radius: radius,