fix(dashboard): show create folder button on mobile in persona manager (#9812)

On small screens, the sidebar is hidden (d-none d-md-flex), so the
"create folder" entry in the toolbar dropdown is the only way for
mobile users to create folders. The current v-if="!hasFolders"
condition prevents it from showing when folders already exist.

dashboard/src/views/persona/PersonaManager.vue

@@ -36,7 +36,7 @@
                 </v-list-item-title>
               </v-list-item>
               <v-list-item
-                v-if="!hasFolders"
+                v-if="!hasFolders || $vuetify.display.smAndDown"
                 prepend-icon="mdi-folder-plus"
                 @click="showCreateFolderDialog = true"
               >