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/menu_drawer.dart

@@ -1,6 +1,6 @@
 import 'package:flutter/material.dart';
 import 'package:notas/models/category.dart';
-import 'package:notas/theme/app_colors.dart';
+import 'package:notas/theme/app_palette.dart';
 import 'package:notas/widgets/category_style.dart';
 
 class MenuDrawer extends StatelessWidget {
@@ -21,10 +21,12 @@ class MenuDrawer extends StatelessWidget {
 
   @override
   Widget build(BuildContext context) {
+    final AppPalette palette = Theme.of(context).extension<AppPalette>()!;
+
     return Container(
-      decoration: const BoxDecoration(
-        color: AppColors.drawerBackground,
-        border: Border(right: BorderSide(color: AppColors.border, width: 0.5)),
+      decoration: BoxDecoration(
+        color: palette.drawerBackground,
+        border: Border(right: BorderSide(color: palette.border, width: 0.5)),
       ),
       child: Column(
         children: [
@@ -59,12 +61,10 @@ class MenuDrawer extends StatelessWidget {
                                 ? null
                                 : () => onEditCategory?.call(category),
                             iconColor: Color(
-                              category.colorValue ??
-                                  AppColors.categoryFallback.value,
+                              category.colorValue ?? palette.accent.value,
                             ),
                             textColor: Color(
-                              category.colorValue ??
-                                  AppColors.categoryFallback.value,
+                              category.colorValue ?? palette.accent.value,
                             ),
                             trailing: IconButton(
                               padding: const EdgeInsets.all(8),
@@ -72,9 +72,9 @@ class MenuDrawer extends StatelessWidget {
                                 minWidth: 0,
                                 minHeight: 0,
                               ),
-                              icon: const Icon(
+                              icon: Icon(
                                 Icons.more_vert,
-                                color: AppColors.textSecondary,
+                                color: palette.textSecondary,
                                 size: 20,
                               ),
                               onPressed: () => onEditCategory?.call(category),
@@ -97,10 +97,10 @@ class MenuDrawer extends StatelessWidget {
             label: 'Mis notas borradas',
             selected: selectedItem == 'deleted_notes',
             onTap: () => onMenuItemTapped?.call('deleted_notes'),
-            iconColor: AppColors.destructiveAccent,
-            textColor: AppColors.destructiveAccent,
+            iconColor: palette.destructiveAccent,
+            textColor: palette.destructiveAccent,
           ),
-          const Divider(color: AppColors.border, height: 16),
+          Divider(color: palette.border, height: 16),
           _MenuItemTile(
             icon: Icons.settings,
             label: 'Configuración',
@@ -143,13 +143,12 @@ class _MenuItemTileState extends State<_MenuItemTile> {
 
   @override
   Widget build(BuildContext context) {
+    final AppPalette palette = Theme.of(context).extension<AppPalette>()!;
     final bool active = widget.selected || _hovering;
-    final Color backgroundColor = active
-        ? AppColors.hover
-        : AppColors.transparent;
+    final Color backgroundColor = active ? palette.hover : palette.transparent;
     final Color foregroundColor = active
-        ? AppColors.textPrimary
-        : AppColors.textSecondary;
+        ? palette.textPrimary
+        : palette.textSecondary;
     final Widget? trailing = _hovering ? widget.trailing : null;
 
     return MouseRegion(