refactor: new chat page text

lib/core/utils/user_display_name.dart

@@ -0,0 +1,85 @@
+import '../models/user.dart' as models;
+
+String deriveUserDisplayName(dynamic user, {String fallback = 'User'}) {
+  if (user == null) {
+    return fallback;
+  }
+
+  String normalize(String? value) {
+    if (value == null) return '';
+    final trimmed = value.trim();
+    return trimmed;
+  }
+
+  String emailFallback(String? email) {
+    final trimmed = normalize(email);
+    if (trimmed.isEmpty) return '';
+    final at = trimmed.indexOf('@');
+    if (at > 0) {
+      return trimmed.substring(0, at);
+    }
+    return trimmed;
+  }
+
+  if (user is models.User) {
+    final name = normalize(user.name);
+    if (name.isNotEmpty) return name;
+
+    final username = normalize(user.username);
+    if (username.isNotEmpty) return username;
+
+    final email = emailFallback(user.email);
+    if (email.isNotEmpty) return email;
+
+    return fallback;
+  }
+
+  if (user is Map) {
+    String? pick(Map<dynamic, dynamic> source) {
+      for (final key in const [
+        'name',
+        'display_name',
+        'preferred_username',
+        'username',
+      ]) {
+        final value = source[key];
+        final normalized = normalize(value is String ? value : null);
+        if (normalized.isNotEmpty) {
+          return normalized;
+        }
+      }
+      return null;
+    }
+
+    final topLevel = pick(user);
+    if (topLevel != null && topLevel.isNotEmpty) {
+      return topLevel;
+    }
+
+    final nestedUser = user['user'];
+    if (nestedUser is Map) {
+      final nested = pick(nestedUser);
+      if (nested != null && nested.isNotEmpty) {
+        return nested;
+      }
+      final email = emailFallback(nestedUser['email'] as String?);
+      if (email.isNotEmpty) {
+        return email;
+      }
+    }
+
+    final email = emailFallback(user['email'] as String?);
+    if (email.isNotEmpty) {
+      return email;
+    }
+
+    return fallback;
+  }
+
+  final asString = normalize(user.toString());
+  if (asString.isNotEmpty) {
+    return asString;
+  }
+
+  return fallback;
+}