feat(profile): Material default avatar + square photo crop

Drop the DiceBear generated avatar (and dicebear_core/dicebear_styles/
flutter_svg): the default is again a Material coloured-initial disc from
the pubkey. Picking a photo now goes through a square crop step
(crop_your_image — pure Flutter, all platforms incl. desktop, Apache-2.0,
only pulls the image package we already had) before the 24 KB thumbnail.

apps/app_seeds/test/ui/chat_message_list_test.dart

@@ -124,14 +124,14 @@ void main() {
     await tester.pumpWidget(host(cubit));
     await tester.pump();
 
-    // Both sides carry an avatar, each generated from its own pubkey —
+    // Both sides carry an avatar, and the two people are different colours —
     // so you can tell who said what at a glance.
     expect(find.byType(PeerAvatar), findsNWidgets(2));
-    final generated = tester
-        .widgetList<GeneratedAvatar>(find.byType(GeneratedAvatar))
+    final discs = tester
+        .widgetList<CircleAvatar>(find.byType(CircleAvatar))
         .toList();
-    expect(generated, hasLength(2));
-    expect(generated.first.pubkey, isNot(generated.last.pubkey));
+    expect(discs, hasLength(2));
+    expect(discs.first.backgroundColor, isNot(discs.last.backgroundColor));
   });
 
   testWidgets('a new message lands in view at the bottom, not below the fold', (

apps/app_seeds/test/ui/peer_avatar_test.dart

@@ -36,19 +36,17 @@ void main() {
       home: Scaffold(body: Center(child: child)),
     );
 
-    testWidgets('falls back to a generated avatar keyed by pubkey', (
-      tester,
-    ) async {
+    testWidgets('shows the name initial when known', (tester) async {
       await tester.pumpWidget(host(PeerAvatar(pubkey: 'aa', name: 'rosa')));
-      final generated =
-          tester.widget<GeneratedAvatar>(find.byType(GeneratedAvatar));
-      expect(generated.pubkey, 'aa'); // pubkey, not name → stable across renames
-      expect(find.byType(Text), findsNothing);
+      expect(find.text('R'), findsOneWidget); // uppercased first letter
     });
 
-    testWidgets('generates it even when the name is unknown', (tester) async {
+    testWidgets('falls back to a person icon when the name is unknown', (
+      tester,
+    ) async {
       await tester.pumpWidget(host(const PeerAvatar(pubkey: 'aa')));
-      expect(find.byType(GeneratedAvatar), findsOneWidget);
+      expect(find.byIcon(Icons.person_outline), findsOneWidget);
+      expect(find.byType(Text), findsNothing);
     });
 
     testWidgets('renders a seed illustration when the avatar is a token', (
@@ -75,19 +73,19 @@ void main() {
       expect(find.byType(SeedGlyph), findsOneWidget);
     });
 
-    testWidgets('falls back to the generated avatar when nothing is cached', (
+    testWidgets('falls back to the initial when nothing is cached', (
       tester,
     ) async {
       final cache = ProfileCache(InMemorySecretStore());
       await tester.pumpWidget(host(
           CachedAvatar(pubkey: 'peer2', name: 'Bea', cache: cache)));
       await tester.pumpAndSettle();
-      expect(find.byType(GeneratedAvatar), findsOneWidget);
+      expect(find.text('B'), findsOneWidget);
     });
 
-    testWidgets('no cache → the generated avatar', (tester) async {
+    testWidgets('no cache → the coloured-initial disc', (tester) async {
       await tester.pumpWidget(host(const CachedAvatar(pubkey: 'x', name: 'Bea')));
-      expect(find.byType(GeneratedAvatar), findsOneWidget);
+      expect(find.text('B'), findsOneWidget);
     });
   });
 }

apps/app_seeds/test/ui/photo_crop_test.dart

@@ -0,0 +1,48 @@
+import 'dart:typed_data';
+
+import 'package:flutter/material.dart';
+import 'package:flutter_test/flutter_test.dart';
+import 'package:image/image.dart' as img;
+import 'package:tane/ui/photo_crop.dart';
+
+void main() {
+  // A small but real PNG the cropper can decode.
+  final bytes = Uint8List.fromList(
+    img.encodePng(img.Image(width: 32, height: 32)),
+  );
+
+  testWidgets('cropToSquare shows a cancel/confirm UI and cancel returns null', (
+    tester,
+  ) async {
+    Uint8List? result;
+    var returned = false;
+    await tester.pumpWidget(MaterialApp(
+      home: Builder(
+        builder: (context) => Scaffold(
+          body: Center(
+            child: ElevatedButton(
+              onPressed: () async {
+                result = await cropToSquare(context, bytes);
+                returned = true;
+              },
+              child: const Text('open'),
+            ),
+          ),
+        ),
+      ),
+    ));
+
+    await tester.tap(find.text('open'));
+    await tester.pump(); // push the crop route
+    await tester.pump(const Duration(milliseconds: 100));
+
+    expect(find.byKey(const Key('crop.confirm')), findsOneWidget);
+    expect(find.byKey(const Key('crop.cancel')), findsOneWidget);
+
+    await tester.tap(find.byKey(const Key('crop.cancel')));
+    await tester.pump(); // pop the crop route
+
+    expect(returned, isTrue);
+    expect(result, isNull); // cancelling yields no image
+  });
+}