feat(block2): profiles — your identity card + name/about (NIP-01 kind:0)

Drawer 'Profile' is now live.
- commons_core: ProfileTransport + UserProfile + NostrProfileTransport (kind:0
  publish/fetch), exposed as SocialSession.profile. Round-trip tested against the
  in-process relay (fast dart test).
- app: ProfileStore (local name/about, keystore) + ProfileScreen — shows your
  shareable npub with copy, edits display name + 'about', saves locally and (when
  online) publishes kind:0 so peers can recognise you instead of a raw key.
- Drawer 'Profile' -> /profile (gated like Market/Chat).
- i18n en/es/pt. ProfileStore + profile transport covered by plain/dart tests.

Analyzer clean (both packages).

packages/commons_core/lib/commons_core.dart

@@ -18,10 +18,12 @@ export 'src/social/nostr/nostr_channel.dart';
 export 'src/social/nostr/nostr_connection.dart';
 export 'src/social/nostr/nostr_message_transport.dart';
 export 'src/social/nostr/nostr_offer_transport.dart';
+export 'src/social/nostr/nostr_profile_transport.dart';
 export 'src/social/nostr/nostr_trust_transport.dart';
 export 'src/social/nostr/relay_pool.dart';
 export 'src/social/offer.dart';
 export 'src/social/offer_transport.dart';
+export 'src/social/profile_transport.dart';
 export 'src/social/trust_transport.dart';
 export 'src/social/web_of_trust.dart';
 export 'src/value/quantity.dart';

packages/commons_core/lib/src/social/nostr/nostr_profile_transport.dart

@@ -0,0 +1,61 @@
+import 'dart:convert';
+
+import 'package:nostr/nostr.dart';
+
+import '../profile_transport.dart';
+import 'nostr_channel.dart';
+
+/// Nostr NIP-01 kind:0 backend for [ProfileTransport], on the shared channel.
+class NostrProfileTransport implements ProfileTransport {
+  NostrProfileTransport(this._conn);
+
+  final NostrChannel _conn;
+
+  /// NIP-01 set_metadata (replaceable).
+  static const kindMetadata = 0;
+
+  @override
+  Future<void> publish({
+    String name = '',
+    String about = '',
+    String picture = '',
+  }) async {
+    final content = jsonEncode({
+      if (name.isNotEmpty) 'name': name,
+      if (about.isNotEmpty) 'about': about,
+      if (picture.isNotEmpty) 'picture': picture,
+    });
+    final event = Event.from(
+      kind: kindMetadata,
+      content: content,
+      tags: const [],
+      secretKey: _conn.privateKeyHex,
+    );
+    await _conn.publish(event);
+  }
+
+  @override
+  Future<UserProfile?> fetch(String pubkeyHex) async {
+    final events = await _conn.reqOnce(
+      Filter(kinds: const [kindMetadata], authors: [pubkeyHex], limit: 1),
+    );
+    if (events.isEmpty) return null;
+    // Newest wins if several slipped through.
+    events.sort((a, b) => b.createdAt.compareTo(a.createdAt));
+    final event = events.first;
+    try {
+      final map = jsonDecode(event.content) as Map<String, dynamic>;
+      return UserProfile(
+        pubkeyHex: pubkeyHex,
+        name: (map['name'] as String?) ?? '',
+        about: (map['about'] as String?) ?? '',
+        picture: (map['picture'] as String?) ?? '',
+      );
+    } catch (_) {
+      return UserProfile(pubkeyHex: pubkeyHex);
+    }
+  }
+
+  @override
+  Future<void> close() => _conn.close();
+}

packages/commons_core/lib/src/social/profile_transport.dart

@@ -0,0 +1,30 @@
+/// A user's public profile (NIP-01 kind:0 metadata) — the human name others see
+/// instead of a raw key. Only what the person chooses to publish.
+class UserProfile {
+  const UserProfile({
+    required this.pubkeyHex,
+    this.name = '',
+    this.about = '',
+    this.picture = '',
+  });
+
+  final String pubkeyHex;
+  final String name;
+  final String about;
+  final String picture;
+
+  bool get isEmpty => name.isEmpty && about.isEmpty && picture.isEmpty;
+}
+
+/// Publish/fetch public profile metadata. Kind:0 is replaceable — publishing
+/// again overwrites. Part of the social layer (identity is generic core), a
+/// sibling of the offer/message/trust transports over the same connection.
+abstract interface class ProfileTransport {
+  /// Publishes (replaces) this identity's profile.
+  Future<void> publish({String name, String about, String picture});
+
+  /// Fetches [pubkeyHex]'s latest profile, or null if they never published one.
+  Future<UserProfile?> fetch(String pubkeyHex);
+
+  Future<void> close();
+}