feat(branding): replace default Flutter icon with Querya logo

lib/features/help/about_dialog.dart

@@ -48,10 +48,16 @@ class _AboutDialogContentState extends material.State<_AboutDialogContent> {
             padding: const material.EdgeInsets.fromLTRB(24, 28, 24, 8),
             child: material.Column(
               children: [
-                material.Icon(
-                  QueryaIcons.database,
-                  size: 48,
-                  color: wb.accent,
+                material.Image.asset(
+                  'assets/images/querya_logo.png',
+                  width: 56,
+                  height: 56,
+                  filterQuality: material.FilterQuality.medium,
+                  errorBuilder: (_, __, ___) => material.Icon(
+                    QueryaIcons.database,
+                    size: 48,
+                    color: wb.accent,
+                  ),
                 ),
                 const material.SizedBox(height: 16),
                 const Text('Querya').large().semiBold(),

lib/features/settings/preferences_about_section.dart

@@ -45,10 +45,16 @@ class PreferencesAboutSection extends StatelessWidget {
                   ),
                 ),
                 child: material.Center(
-                  child: material.Icon(
-                    QueryaIcons.database,
-                    size: 24,
-                    color: theme.colorScheme.primary,
+                  child: material.Image.asset(
+                    'assets/images/querya_logo.png',
+                    width: 28,
+                    height: 28,
+                    filterQuality: material.FilterQuality.medium,
+                    errorBuilder: (_, __, ___) => material.Icon(
+                      QueryaIcons.database,
+                      size: 24,
+                      color: theme.colorScheme.primary,
+                    ),
                   ),
                 ),
               ),

test/features/help/about_dialog_test.dart

@@ -1,6 +1,5 @@
 import 'package:flutter/material.dart' as material;
 import 'package:flutter_test/flutter_test.dart';
-import 'package:querya_desktop/core/ui/querya_icons.dart';
 import 'package:querya_desktop/features/help/about_dialog.dart';
 
 import '../../support/querya_theme_test_shell.dart';
@@ -23,7 +22,16 @@ void main() {
       await tester.pumpAndSettle();
 
       expect(find.text('Querya'), findsOneWidget);
-      expect(find.byIcon(QueryaIcons.database), findsOneWidget);
+      expect(
+        find.byWidgetPredicate(
+          (w) =>
+              w is material.Image &&
+              w.image is material.AssetImage &&
+              (w.image as material.AssetImage).assetName ==
+                  'assets/images/querya_logo.png',
+        ),
+        findsOneWidget,
+      );
       expect(find.textContaining('Version'), findsOneWidget);
       expect(find.text('Licensed under the MIT License.'), findsOneWidget);
       expect(find.text('View repository'), findsOneWidget);