feat: implement standardized protocol

Signed-off-by: Sebastian <krupinski01@gmail.com>

src/components/settings/DisplaySettings.vue

@@ -12,9 +12,7 @@ const compactMode = ref(false)
 
 const folderViewMode = computed({
   get: () => {
-    const allSettings = settings.value?.all || {}
-    const mailSettings = allSettings.mail || {}
-    return (mailSettings.folderViewMode as FolderViewMode) || 'tree'
+    return (settings.value.get('mail.folderViewMode') as FolderViewMode) || 'tree'
   },
   set: (value: FolderViewMode) => setSetting('mail.folderViewMode', value)
 })