Refactor theme management: Replace AppColors with AppPalette

- Removed AppColors class and migrated all references to AppPalette.
- Updated VaultAccessScreen, MenuDrawer, NoteCard, SearchAppBar, and other widgets to use AppPalette for color management.
- Introduced AppPalette to handle light and dark themes with appropriate color schemes.
- Adjusted theme application in AppTheme to utilize AppPalette extensions.
- Updated tests to reflect changes in theme structure and color references.

lib/widgets/category_style.dart

@@ -1,10 +1,19 @@
 import 'package:flutter/material.dart';
-import 'package:notas/theme/app_colors.dart';
+import 'package:notas/theme/app_palette.dart';
 
 class CategoryStyle {
   CategoryStyle._();
 
-  static const List<Color> colors = AppColors.categoryColors;
+  static const List<Color> colors = AppPalette.defaultCategoryColors;
+
+  static List<Color> colorsOf(BuildContext context) {
+    final AppPalette? palette = Theme.of(context).extension<AppPalette>();
+    if (palette != null) {
+      return palette.categoryColors;
+    }
+
+    return AppPalette.defaultCategoryColors;
+  }
 
   static const List<IconData> icons = <IconData>[
     Icons.label_outline_rounded,