📝 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/i18n/locales/en.json

@@ -1615,6 +1615,7 @@
   "编辑公告": "Edit Notice",
   "公告内容": "Notice Content",
   "请输入公告内容": "Please enter the notice content",
+  "请输入公告内容（支持 Markdown/HTML）": "Please enter the notice content (supports Markdown/HTML)",
   "发布日期": "Publish Date",
   "请选择发布日期": "Please select the publish date",
   "发布时间": "Publish Time",
@@ -1630,6 +1631,7 @@
   "请输入问题标题": "Please enter the question title",
   "回答内容": "Answer Content",
   "请输入回答内容": "Please enter the answer content",
+  "请输入回答内容（支持 Markdown/HTML）": "Please enter the answer content (supports Markdown/HTML)",
   "确定要删除此问答吗？": "Are you sure you want to delete this FAQ?",
   "系统公告管理，可以发布系统通知和重要消息（最多100个，前端显示最新20条）": "System notice management, you can publish system notices and important messages (maximum 100, display latest 20 on the front end)",
   "常见问答管理，为用户提供常见问题的答案（最多50个，前端显示最新20条）": "FAQ management, providing answers to common questions for users (maximum 50, display latest 20 on the front end)",