📝 feat(SettingsAnnouncements/SettingsFAQ): update placeholders & success texts, add Markdown/HTML hint

• SettingsAnnouncements.js
  – Placeholder now states “Supports Markdown/HTML” for both small & expanded editors
  – Success/alert messages unified to use Chinese quotation marks

• SettingsFAQ.js
  – Answer textarea placeholder updated with Markdown/HTML support note
  – Unified success/alert messages punctuation

These tweaks clarify rich-text support and keep UI copy consistent.

web/src/pages/Setting/Dashboard/SettingsFAQ.js

@@ -424,7 +424,7 @@ const SettingsFAQ = ({ options, refresh }) => {
           <Form.TextArea
             field='answer'
             label={t('回答内容')}
-            placeholder={t('请输入回答内容')}
+            placeholder={t('请输入回答内容（支持 Markdown/HTML）')}
             maxCount={1000}
             rows={6}
             rules={[{ required: true, message: t('请输入回答内容') }]}