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/lib/ui/avatar_edit.dart

@@ -2,14 +2,16 @@ import 'package:flutter/material.dart';
 
 import '../i18n/strings.g.dart';
 import '../services/offer_thumbnail.dart' show offerThumbnailDataUri;
+import 'photo_crop.dart';
 import 'photo_pick.dart';
 import 'theme.dart';
 
-/// Lets the user choose a profile avatar: take/pick a photo (shrunk to a tiny
-/// inline thumbnail) or remove it. With no photo, a generated avatar is used.
+/// Lets the user choose a profile avatar: take/pick a photo, square-crop it, and
+/// keep it as a tiny inline thumbnail — or remove it. With no photo, the
+/// coloured-initial disc is used.
 ///
 /// Returns the new avatar value (a `data:` photo thumbnail), an empty string to
-/// clear it (falls back to the generated avatar), or null when cancelled.
+/// clear it (falls back to the coloured-initial disc), or null when cancelled.
 Future<String?> showAvatarPicker(
   BuildContext context, {
   required String current,
@@ -37,11 +39,11 @@ Future<String?> showAvatarPicker(
                 title: Text(t.avatar.fromPhoto),
                 onTap: () async {
                   final bytes = await pickPhoto(sheetContext);
-                  if (bytes == null) return;
-                  final uri = offerThumbnailDataUri(bytes, maxBytes: 24000);
-                  if (sheetContext.mounted) {
-                    Navigator.of(sheetContext).pop(uri ?? '');
-                  }
+                  if (bytes == null || !sheetContext.mounted) return;
+                  final cropped = await cropToSquare(sheetContext, bytes);
+                  if (cropped == null || !sheetContext.mounted) return;
+                  final uri = offerThumbnailDataUri(cropped, maxBytes: 24000);
+                  Navigator.of(sheetContext).pop(uri ?? '');
                 },
               ),
               if (current.isNotEmpty) ...[

apps/app_seeds/lib/ui/peer_avatar.dart

@@ -1,7 +1,4 @@
-import 'package:dicebear_core/dicebear_core.dart' show Avatar, Style;
-import 'package:dicebear_styles/thumbs.dart';
 import 'package:flutter/material.dart';
-import 'package:flutter_svg/flutter_svg.dart';
 
 import '../services/offer_thumbnail.dart' show decodeDataUri;
 import '../services/profile_cache.dart';
@@ -9,10 +6,11 @@ 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 [GeneratedAvatar] drawn deterministically from
-/// their [pubkey]. Same pubkey → same picture on every device, so a person
-/// stays visually recognizable without sharing anything.
+/// `data:` photo thumbnail, or a legacy `tane:seed:<glyph>` illustration) it's
+/// shown; otherwise it falls back to a standard disc coloured deterministically
+/// from their [pubkey], carrying the first letter of their [name] (a person icon
+/// when unknown). Same pubkey → same colour on every device, so a person stays
+/// visually recognizable without sharing anything.
 class PeerAvatar extends StatelessWidget {
   const PeerAvatar({
     required this.pubkey,
@@ -25,7 +23,7 @@ class PeerAvatar extends StatelessWidget {
   final String pubkey;
   final String? name;
 
-  /// The person's chosen avatar value; null/empty → the [GeneratedAvatar].
+  /// The person's chosen avatar value; null/empty → the coloured-initial disc.
   final String? picture;
   final double radius;
 
@@ -49,61 +47,35 @@ class PeerAvatar extends StatelessWidget {
       }
     }
 
-    return GeneratedAvatar(pubkey: pubkey, name: name, radius: radius);
-  }
-}
-
-/// The `thumbs` DiceBear style, parsed once — [Style.parse] validates the style
-/// definition against its schema, which is not free to repeat per build.
-final _thumbsStyle = Style.parse(thumbs);
-
-/// Rendered-SVG memo keyed by pubkey, so a person's avatar is generated once and
-/// reused across every rebuild and list row rather than re-rendered each time.
-final _svgCache = <String, String>{};
-
-/// Strips the `<metadata>` block (the style's CC0 licence notice) that
-/// flutter_svg cannot parse and logs a warning for; CC0 requires no attribution
-/// in the rendered image, and the licence still ships with the package source.
-final _metadataElement = RegExp(r'<metadata\b[^>]*>.*?</metadata>', dotAll: true);
-
-String _renderThumbs(String pubkey) =>
-    Avatar(_thumbsStyle, {'seed': pubkey}).svg.replaceAll(_metadataElement, '');
-
-/// The deterministic default avatar for a person with no chosen [picture]: a
-/// friendly DiceBear "thumbs" face (CC0) seeded from their [pubkey], so the same
-/// key yields the same face on every device with nothing shared. Rendered as an
-/// SVG (no network, no assets). Exposes [pubkey] so call sites/tests can find it.
-class GeneratedAvatar extends StatelessWidget {
-  const GeneratedAvatar({
-    required this.pubkey,
-    this.name,
-    this.radius = 14,
-    super.key,
-  });
-
-  final String pubkey;
-  final String? name;
-  final double radius;
-
-  @override
-  Widget build(BuildContext context) {
-    final svg = _svgCache[pubkey] ??= _renderThumbs(pubkey);
-    return Semantics(
-      label: name,
-      image: true,
-      child: ClipOval(
-        child: SizedBox.square(
-          dimension: radius * 2,
-          child: SvgPicture.string(svg, fit: BoxFit.cover),
-        ),
-      ),
+    final letter = _initial(name);
+    return CircleAvatar(
+      radius: radius,
+      backgroundColor: peerAvatarColor(pubkey),
+      child: letter == null
+          ? Icon(Icons.person_outline, size: radius, color: Colors.white)
+          : Text(
+              letter,
+              style: TextStyle(
+                color: Colors.white,
+                fontSize: radius,
+                fontWeight: FontWeight.w600,
+              ),
+            ),
     );
   }
+
+  static String? _initial(String? name) {
+    if (name == null) return null;
+    final trimmed = name.trim();
+    if (trimmed.isEmpty) return null;
+    // characters.first handles emoji/combining marks safely.
+    return trimmed.characters.first.toUpperCase();
+  }
 }
 
 /// A [PeerAvatar] that looks the person's published avatar up from the
-/// [ProfileCache] (their kind:0 `picture`), falling back to the generated
-/// pattern while it loads or when none is cached / no cache is available. Use at
+/// [ProfileCache] (their kind:0 `picture`), falling back to the coloured-initial
+/// disc while it loads or when none is cached / no cache is available. Use at
 /// list/row sites (one avatar each); for many avatars of the same few people
 /// (chat bubbles) resolve the picture once into state instead.
 class CachedAvatar extends StatelessWidget {

apps/app_seeds/lib/ui/photo_crop.dart

@@ -0,0 +1,87 @@
+import 'dart:typed_data';
+
+import 'package:crop_your_image/crop_your_image.dart';
+import 'package:flutter/material.dart';
+
+import 'theme.dart';
+
+/// Lets the user square-crop the picked [bytes] before it's saved as an avatar.
+/// Returns the cropped image bytes, or null if cancelled. Pure Flutter (works on
+/// every platform, desktop included) — no native cropper, no plaintext on disk.
+Future<Uint8List?> cropToSquare(BuildContext context, Uint8List bytes) {
+  return Navigator.of(context).push<Uint8List>(
+    MaterialPageRoute(
+      fullscreenDialog: true,
+      builder: (context) => _CropPage(bytes: bytes),
+    ),
+  );
+}
+
+class _CropPage extends StatefulWidget {
+  const _CropPage({required this.bytes});
+
+  final Uint8List bytes;
+
+  @override
+  State<_CropPage> createState() => _CropPageState();
+}
+
+class _CropPageState extends State<_CropPage> {
+  final _controller = CropController();
+  var _cropping = false;
+
+  @override
+  Widget build(BuildContext context) {
+    return Scaffold(
+      backgroundColor: Colors.black,
+      appBar: AppBar(
+        backgroundColor: Colors.black,
+        foregroundColor: Colors.white,
+        leading: IconButton(
+          key: const Key('crop.cancel'),
+          icon: const Icon(Icons.close),
+          onPressed: () => Navigator.of(context).pop(),
+        ),
+        actions: [
+          if (_cropping)
+            const Padding(
+              padding: EdgeInsets.all(14),
+              child: SizedBox(
+                width: 20,
+                height: 20,
+                child: CircularProgressIndicator(strokeWidth: 2),
+              ),
+            )
+          else
+            IconButton(
+              key: const Key('crop.confirm'),
+              icon: const Icon(Icons.check),
+              onPressed: () {
+                setState(() => _cropping = true);
+                _controller.crop();
+              },
+            ),
+        ],
+      ),
+      body: Crop(
+        image: widget.bytes,
+        controller: _controller,
+        aspectRatio: 1,
+        withCircleUi: true,
+        baseColor: Colors.black,
+        maskColor: Colors.black.withValues(alpha: 0.6),
+        cornerDotBuilder: (size, edgeAlignment) =>
+            const DotControl(color: seedGreen),
+        onCropped: (result) {
+          if (!mounted) return;
+          switch (result) {
+            case CropSuccess(:final croppedImage):
+              Navigator.of(context).pop(croppedImage);
+            case CropFailure():
+              setState(() => _cropping = false);
+          }
+        },
+      ),
+    );
+  }
+}