fix(dashboard): Certain menus inside of modals are hidden (#875)

* fix: update z-index utility class for Select component across tag category and tutor selection views

* refactor: standardize z-index management using ui:z-menu-elevated, ui:z-app-bar, ui:z-app-bar-elevated and ui:z-modal classes across UI components

---------

Co-authored-by: richardkenneth <richard-kenneth@users.noreply.github.com>

apps/dashboard/src/lib/features/course/components/exercise/mark-exercise-modal.svelte

@@ -296,7 +296,7 @@
               >
                 <EllipsisVerticalIcon class="h-5 w-5" />
               </DropdownMenu.Trigger>
-              <DropdownMenu.Content align="end" class="z-menu-elevated">
+              <DropdownMenu.Content align="end">
                 <DropdownMenu.Item
                   class="text-red-600"
                   onclick={() => {
@@ -366,7 +366,7 @@
               <Select.Trigger class="w-full">
                 {status.text}
               </Select.Trigger>
-              <Select.Content class="z-menu-elevated">
+              <Select.Content>
                 {#each SELECTABLE_STATUS as statusOption}
                   <Select.Item value={statusOption.id.toString()}>
                     {statusOption.text}