[6.x] Fix folders not displaying in Bard link stack selector

[duncanmcclean]

This pull request fixes an issue where folders weren't displaying properly in the asset selector when adding a link in Bard.

This was happening because the columns prop was missing, which the Table component relies on to create "fake" cells in folder rows:

cms/resources/js/components/assets/Browser/Table.vue

Lines 25 to 58 in a397f89

	<td v-for="column in visibleColumns">
	<template v-if="column.field === 'basename'">
	<a class="group flex cursor-pointer items-center" @click="selectFolder(folder.path)">
	<file-icon
	extension="folder"
	class="me-2 inline-block size-8 text-blue-400/90 group-hover:text-blue-400"
	/>
	{{ folder.basename }}
	</a>
	</template>
	</td>
	<td class="actions-column pe-3!">
	<ItemActions
	:url="folderActionUrl"
	:actions="folder.actions"
	:item="folder.path"
	@started="actionStarted"
	@completed="actionCompleted"
	v-slot="{ actions }"
	>
	<Dropdown placement="left-start" v-if="folderActions(folder).length">
	<DropdownMenu>
	<DropdownItem
	v-for="action in actions"
	:key="action.handle"
	:text="__(action.title)"
	:icon="action.icon"
	:variant="action.dangerous ? 'destructive' : 'default'"
	@click="action.run"
	/>
	</DropdownMenu>
	</Dropdown>
	</ItemActions>
	</td>

Fixes #13980.

Before

After