feat: Display received time and fix timestamp timezone conversion.

frontend/src/i18n/index.js

@@ -24,6 +24,7 @@ const messages = {
       selectMail: '请从选择一封邮件查看',
       from: '发件人',
       to: '收件人',
+      received_at: '收件时间',
       attachments: '附件',
       delete: '删除',
       clearInbox: '清空收件箱',
@@ -68,6 +69,7 @@ const messages = {
       selectMail: 'Please select an email to view',
       from: 'From',
       to: 'To',
+      received_at: 'Received At',
       attachments: 'Attachments',
       delete: 'Delete',
       clearInbox: 'Clear Inbox',

frontend/src/views/Home.vue

@@ -64,6 +64,7 @@
                 <h3>{{ selectedMessage.subject }}</h3>
                 <p class="from-line"><strong>{{ $t('home.from') }}:</strong> {{ selectedMessage.sender }}</p>
                 <p><strong>{{ $t('home.to') }}:</strong> {{ selectedMessage.recipient }}</p>
+                <p><strong>{{ $t('home.received_at') }}:</strong> {{ selectedMessage.received_at }}</p>
               </div>
               <div class="header-actions">
                 <button @click="deleteMessage(selectedMessage.id)" :title="$t('home.delete')">