Refactor theme colors and styles across the application

- Introduced AppColors class to centralize color definitions for better maintainability and consistency.
- Updated various screens (Settings, Vault Access, Note Card, etc.) to use AppColors for styling instead of hardcoded colors.
- Enhanced UI elements with improved color contrast and accessibility.
- Replaced gradient backgrounds with defined color schemes for a cohesive look.
- Refactored button styles and text colors to align with the new theme structure.

lib/widgets/menu_drawer.dart

@@ -1,5 +1,6 @@
 import 'package:flutter/material.dart';
 import 'package:notas/models/category.dart';
+import 'package:notas/theme/app_colors.dart';
 import 'package:notas/widgets/category_style.dart';
 
 class MenuDrawer extends StatelessWidget {
@@ -22,10 +23,8 @@ class MenuDrawer extends StatelessWidget {
   Widget build(BuildContext context) {
     return Container(
       decoration: const BoxDecoration(
-        color: Color.fromARGB(255, 30, 31, 35),
-        border: Border(
-          right: BorderSide(color: Colors.white12, width: 0.5),
-        ),
+        color: AppColors.drawerBackground,
+        border: Border(right: BorderSide(color: AppColors.border, width: 0.5)),
       ),
       child: Column(
         children: [
@@ -50,7 +49,7 @@ class MenuDrawer extends StatelessWidget {
                               CategoryStyle.iconForCodePoint(
                                 category.iconCodePoint,
                               );
-                          
+
                           return _MenuItemTile(
                             icon: categoryIcon,
                             label: category.name,
@@ -59,8 +58,14 @@ class MenuDrawer extends StatelessWidget {
                             onLongPress: onEditCategory == null
                                 ? null
                                 : () => onEditCategory?.call(category),
-                            iconColor: Color(category.colorValue ?? 0xFFFFC107),
-                            textColor: Color(category.colorValue ?? 0xFFFFC107),
+                            iconColor: Color(
+                              category.colorValue ??
+                                  AppColors.categoryFallback.value,
+                            ),
+                            textColor: Color(
+                              category.colorValue ??
+                                  AppColors.categoryFallback.value,
+                            ),
                             trailing: IconButton(
                               padding: const EdgeInsets.all(8),
                               constraints: const BoxConstraints(
@@ -69,7 +74,7 @@ class MenuDrawer extends StatelessWidget {
                               ),
                               icon: const Icon(
                                 Icons.more_vert,
-                                color: Colors.white70,
+                                color: AppColors.textSecondary,
                                 size: 20,
                               ),
                               onPressed: () => onEditCategory?.call(category),
@@ -92,10 +97,10 @@ class MenuDrawer extends StatelessWidget {
             label: 'Mis notas borradas',
             selected: selectedItem == 'deleted_notes',
             onTap: () => onMenuItemTapped?.call('deleted_notes'),
-            iconColor: Colors.redAccent,
-            textColor: Colors.redAccent,
+            iconColor: AppColors.destructiveAccent,
+            textColor: AppColors.destructiveAccent,
           ),
-          const Divider(color: Colors.white12, height: 16),
+          const Divider(color: AppColors.border, height: 16),
           _MenuItemTile(
             icon: Icons.settings,
             label: 'Configuración',
@@ -140,9 +145,11 @@ class _MenuItemTileState extends State<_MenuItemTile> {
   Widget build(BuildContext context) {
     final bool active = widget.selected || _hovering;
     final Color backgroundColor = active
-        ? Colors.white.withValues(alpha: 0.10)
-        : Colors.transparent;
-    final Color foregroundColor = active ? Colors.white : Colors.white70;
+        ? AppColors.hover
+        : AppColors.transparent;
+    final Color foregroundColor = active
+        ? AppColors.textPrimary
+        : AppColors.textSecondary;
     final Widget? trailing = _hovering ? widget.trailing : null;
 
     return MouseRegion(
@@ -155,11 +162,7 @@ class _MenuItemTileState extends State<_MenuItemTile> {
       child: AnimatedContainer(
         duration: const Duration(milliseconds: 180),
         curve: Curves.easeOutCubic,
-        margin: const EdgeInsets.only(
-          right: 8,
-          top: 2,
-          bottom: 2,
-        ),
+        margin: const EdgeInsets.only(right: 8, top: 2, bottom: 2),
         child: Material(
           color: backgroundColor,
           borderRadius: const BorderRadius.only(
@@ -169,11 +172,17 @@ class _MenuItemTileState extends State<_MenuItemTile> {
           clipBehavior: Clip.antiAlias,
           child: ListTile(
             contentPadding: const EdgeInsets.only(left: 16, right: 8),
-            leading: Icon(widget.icon, color: widget.iconColor ?? foregroundColor),
+            leading: Icon(
+              widget.icon,
+              color: widget.iconColor ?? foregroundColor,
+            ),
             trailing: trailing,
             title: Text(
               widget.label,
-              style: TextStyle(color: widget.textColor ?? foregroundColor, fontSize: 14),
+              style: TextStyle(
+                color: widget.textColor ?? foregroundColor,
+                fontSize: 14,
+              ),
             ),
             onTap: widget.onTap,
             onLongPress: widget.onLongPress,