fix(export): keep session row actions sticky in viewport

src/pages/ExportPage.scss

@@ -2480,11 +2480,13 @@
   align-items: flex-end;
   gap: 4px;
   width: var(--contacts-action-col-width);
+  min-width: var(--contacts-action-col-width);
   flex-shrink: 0;
   position: sticky;
   right: 0;
-  z-index: 6;
+  z-index: 10;
   background: var(--bg-primary);
+  will-change: transform;
 
   &::before {
     content: '';