refactor: simplify multiSelect module (remove duplicates, etc)

- remove duplicate code
- use one uniq selection bar (for both list & grid view)

static/index.html

@@ -255,6 +255,8 @@
                 <span class="breadcrumb-item" data-i18n="breadcrumb.home">Home</span>
             </div>
 
+            <div id="batch-selection-bar" class="batch-selection-bar"></div>
+
             <!-- Files Container -->
             <div class="files-container">
                 <!-- Grid View -->
@@ -332,5 +334,6 @@
 
     <!-- Upload Progress Toast (hidden – driven by notification bell) -->
     <div class="upload-toast hidden" id="upload-toast"></div>
+
 </body>
 </html>