Fix notification deletion bug: save {} instead of [] when list is empty

When all notifications are deleted, the persistentNotifications array
becomes empty ([]). The backend doesn't accept an empty array as a
valid value, requiring an empty object ({}) instead. This fix modifies
both index.vue and UrgentTestDialog.vue to save {} when the
notification list is empty.

Co-authored-by: Sunwuyuan <88357633+Sunwuyuan@users.noreply.github.com>

src/components/settings/cards/EditSettingsCard.vue

@@ -1,28 +1,30 @@
 <template>
-  <settings-card icon="mdi-cog" title="编辑设置">
+  <settings-card
+    icon="mdi-cog"
+    title="编辑设置"
+  >
     <v-list>
-      <setting-item :setting-key="'edit.autoSave'"/>
+      <setting-item :setting-key="'edit.autoSave'" />
 
 
-      <v-divider class="my-2"/>
-      <setting-item :setting-key="'edit.blockNonTodayAutoSave'"/>
+      <v-divider class="my-2" />
+      <setting-item :setting-key="'edit.blockNonTodayAutoSave'" />
 
 
-      <v-divider class="my-2"/>
-      <setting-item :setting-key="'edit.confirmNonTodaySave'"/>
+      <v-divider class="my-2" />
+      <setting-item :setting-key="'edit.confirmNonTodaySave'" />
 
 
-      <v-divider class="my-2"/>
-      <setting-item :setting-key="'edit.refreshBeforeEdit'"/>
+      <v-divider class="my-2" />
+      <setting-item :setting-key="'edit.refreshBeforeEdit'" />
 
 
-      <v-divider class="my-2"/>
-      <setting-item :setting-key="'edit.autoSavePromptText'"/>
+      <v-divider class="my-2" />
+      <setting-item :setting-key="'edit.autoSavePromptText'" />
 
 
-      <v-divider class="my-2"/>
-      <setting-item :setting-key="'edit.manualSavePromptText'"/>
-
+      <v-divider class="my-2" />
+      <setting-item :setting-key="'edit.manualSavePromptText'" />
     </v-list>
   </settings-card>
 </template>