perf: improve usage of the card component in some pages (#839)

#### What type of PR is this?

/kind improvement

#### What this PR does / why we need it:

优化部分页面 VCard 组件的用法，修复样式问题。

#### Which issue(s) this PR fixes:

Fixes https://github.com/halo-dev/halo/issues/3226

#### Screenshots:

before:

<img width="1417" alt="image" src="https://user-images.githubusercontent.com/21301288/217179383-d1dff4f5-4350-4881-aed6-c6bf2cc184c5.png">

after:

<img width="1430" alt="image" src="https://user-images.githubusercontent.com/21301288/217179173-f61cf787-f34f-43a3-88c3-08fac6c31879.png">

#### Special notes for your reviewer:

测试方式：

1. 检查主题详情页面、插件详情页面、系统设置页面的内容区域，底部的圆角是否生效。

#### Does this PR introduce a user-facing change?

```release-note
优化 Console 端主题详情、插件详情、系统设置中卡片组件的样式。
```

src/modules/interface/themes/layouts/ThemeLayout.vue

@@ -227,7 +227,6 @@ onMounted(() => {
               @change="handleTabChange"
             ></VTabbar>
           </template>
-        </VCard>
           <div class="bg-white">
             <RouterView :key="activeTab" v-slot="{ Component }">
               <template v-if="Component">
@@ -240,6 +239,7 @@ onMounted(() => {
               </template>
             </RouterView>
           </div>
+        </VCard>
       </div>
     </div>
 

src/modules/system/plugins/layouts/PluginLayout.vue

@@ -171,7 +171,6 @@ watch([() => route.name, () => route.params], () => {
             @change="handleTabChange"
           ></VTabbar>
         </template>
-      </VCard>
         <div class="bg-white">
           <RouterView :key="activeTab" v-slot="{ Component }">
             <template v-if="Component">
@@ -184,6 +183,7 @@ watch([() => route.name, () => route.params], () => {
             </template>
           </RouterView>
         </div>
+      </VCard>
     </div>
   </BasicLayout>
 </template>

src/modules/system/settings/layouts/SystemSettingsLayout.vue

@@ -109,7 +109,6 @@ watch([() => route.name, () => route.params], async () => {
             @change="handleTabChange"
           ></VTabbar>
         </template>
-      </VCard>
         <div class="bg-white">
           <RouterView :key="activeTab" v-slot="{ Component }">
             <template v-if="Component">
@@ -122,6 +121,7 @@ watch([() => route.name, () => route.params], async () => {
             </template>
           </RouterView>
         </div>
+      </VCard>
     </div>
   </BasicLayout>
 </template>