style(ui-core): FilterSelect helper text moves to the popover footer

The legacy dropdown pinned its helper line under the scrollable list; only
the options scroll, the helper stays visible.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

Author: harsh-vador

openmetadata-ui-core-components/src/main/resources/ui/src/components/application/filter-select/filter-select.tsx

@@ -378,12 +378,6 @@ export const FilterSelect = ({
           </div>
         )}
 
-        {helperText !== undefined && (
-          <div className="tw:px-4 tw:pb-2 tw:text-xs tw:text-tertiary">
-            {helperText}
-          </div>
-        )}
-
         {showSelectAllRow && (
           <div className="tw:px-4 tw:py-2">
             <Checkbox
@@ -441,6 +435,12 @@ export const FilterSelect = ({
           </Dropdown.Menu>
         )}
 
+        {helperText !== undefined && (
+          <div className="tw:border-t tw:border-secondary tw:px-3 tw:py-2 tw:text-xs tw:text-tertiary">
+            {helperText}
+          </div>
+        )}
+
         {showFooter && (
           <div className="tw:flex tw:items-center tw:justify-between tw:gap-2 tw:border-t tw:border-secondary tw:p-2">
             <Button