Refactor SettingsScreen and SearchAppBar: remove unused menu logic and enhance navigation features

lib/widgets/search_app_bar.dart

@@ -4,6 +4,9 @@ class SearchAppBar extends StatefulWidget {
   const SearchAppBar({
     super.key,
     this.onMenuPressed,
+    this.onLeadingPressed,
+    this.leadingIcon = Icons.menu,
+    this.leadingTooltip = 'Menú',
     this.onSearchChanged,
     this.searchHint = 'Buscar notas...',
     this.showSearch = true,
@@ -11,6 +14,9 @@ class SearchAppBar extends StatefulWidget {
   });
 
   final VoidCallback? onMenuPressed;
+  final VoidCallback? onLeadingPressed;
+  final IconData leadingIcon;
+  final String leadingTooltip;
   final ValueChanged<String>? onSearchChanged;
   final String searchHint;
   final bool showSearch;
@@ -50,11 +56,10 @@ class _SearchAppBarState extends State<SearchAppBar> {
       padding: const EdgeInsets.only(left: 16, right: 16, top: 7, bottom: 7),
       child: Row(
         children: [
-          // Menu button (fixed on left)
           IconButton(
-            onPressed: widget.onMenuPressed,
-            icon: const Icon(Icons.menu, color: Colors.white70, size: 20),
-            tooltip: 'Menú',
+            onPressed: widget.onLeadingPressed ?? widget.onMenuPressed,
+            icon: Icon(widget.leadingIcon, color: Colors.white70, size: 20),
+            tooltip: widget.leadingTooltip,
             splashRadius: 18,
             constraints: const BoxConstraints(minWidth: 40, minHeight: 40),
           ),