implemented comprehensive accessibility (A11y) support across the app

lib/widget/user_avatar.dart

@@ -10,6 +10,7 @@ import 'package:http/http.dart' as http;
 import '../model/account_data.dart';
 import '../model/endpoint_data.dart';
 import '../push/push_avatar.dart';
+import 'a11y/a11y_labels.dart';
 import 'avatar_disk_cache.dart';
 
 class UserAvatar extends StatefulWidget {
@@ -17,6 +18,10 @@ class UserAvatar extends StatefulWidget {
   final bool isGroup;
   final int size;
 
+  /// Screenreader-Beschreibung. Aufrufer, die den Namen kennen, sollten ihn
+  /// mitgeben; sonst greift ein generisches „Profilbild"/„Gruppenbild".
+  final String? semanticLabel;
+
   /// Server-side pixel size requested for user avatars. `null` lets the
   /// widget pick `(size * 4).clamp(64, 1024)` — enough headroom for typical
   /// device pixel ratios. Group avatars ignore this (Spreed serves one
@@ -28,6 +33,7 @@ class UserAvatar extends StatefulWidget {
     this.isGroup = false,
     this.size = 20,
     this.requestSize,
+    this.semanticLabel,
     super.key,
   });
 
@@ -225,7 +231,9 @@ class _UserAvatarState extends State<UserAvatar> {
     final pending = _pendingAvatars.putIfAbsent(url, () {
       final future = _fetch(url);
       future.whenComplete(() {
-        if (identical(_pendingAvatars[url], future)) _pendingAvatars.remove(url);
+        if (identical(_pendingAvatars[url], future)) {
+          _pendingAvatars.remove(url);
+        }
       });
       return future;
     });
@@ -345,12 +353,24 @@ class _UserAvatarState extends State<UserAvatar> {
       );
     }
 
-    return CircleAvatar(
-      radius: radius,
-      backgroundColor: theme.primaryColor,
-      foregroundColor: Colors.white,
-      child: ClipOval(
-        child: SizedBox(width: radius * 2, height: radius * 2, child: content),
+    return Semantics(
+      image: true,
+      label:
+          widget.semanticLabel ??
+          (widget.isGroup
+              ? A11yLabels.groupPicture
+              : A11yLabels.profilePicture),
+      child: CircleAvatar(
+        radius: radius,
+        backgroundColor: theme.primaryColor,
+        foregroundColor: Colors.white,
+        child: ClipOval(
+          child: SizedBox(
+            width: radius * 2,
+            height: radius * 2,
+            child: content,
+          ),
+        ),
       ),
     );
   }