Fix dark mode visibility for all toolbar buttons and icons

- Fixed all formatting toolbar buttons to be visible in dark mode
- Added proper text colors (gray-700/gray-300) to all toolbar icons
- Fixed sync and new note button icons in sidebar
- Fixed divider colors between button groups
- All UI elements now properly visible in both light and dark modes

src/components/NotesList.tsx

@@ -74,7 +74,7 @@ export function NotesList({
               title="Sync with Server"
             >
               <svg 
-                className={`w-5 h-5 ${isSyncing ? 'animate-spin' : ''}`} 
+                className={`w-5 h-5 text-gray-700 dark:text-gray-300 ${isSyncing ? 'animate-spin' : ''}`} 
                 fill="none" 
                 stroke="currentColor" 
                 viewBox="0 0 24 24"
@@ -87,7 +87,7 @@ export function NotesList({
               className="p-2 hover:bg-gray-200 dark:hover:bg-gray-700 rounded-lg transition-colors"
               title="New Note"
             >
-              <svg className="w-5 h-5" fill="none" stroke="currentColor" viewBox="0 0 24 24">
+              <svg className="w-5 h-5 text-gray-700 dark:text-gray-300" fill="none" stroke="currentColor" viewBox="0 0 24 24">
                 <path strokeLinecap="round" strokeLinejoin="round" strokeWidth={2} d="M12 4v16m8-8H4" />
               </svg>
             </button>