feat(mail): 升级写信编辑器并移除 Markdown 依赖。

- 将正文编辑器改为富文本 `contentEditable`，支持字体、字号、颜色、高亮、对齐、列表、缩进等格式化操作。
- 新增抄送/密送显示切换与“分别发送”能力，优化收件人发送方式。
- 移除 `marked` 依赖，并同步精简 `turnstile-box` 的边框样式。

apps/web/package-lock.json

@@ -25,7 +25,6 @@
         "clsx": "2.1.1",
         "dompurify": "3.4.10",
         "lucide-react": "^0.468.0",
-        "marked": "18.0.5",
         "qrcode.react": "^4.2.0",
         "react": "18.3.1",
         "react-dom": "18.3.1",
@@ -4056,18 +4055,6 @@
         "react": "^16.5.1 || ^17.0.0 || ^18.0.0 || ^19.0.0-rc"
       }
     },
-    "node_modules/marked": {
-      "version": "18.0.5",
-      "resolved": "https://registry.npmjs.org/marked/-/marked-18.0.5.tgz",
-      "integrity": "sha512-S6GcvALHg6K4ohtu4E7x0a1AqhAjp6cV8KhLSyN9qVapnzJkusVBxZRcIU9AeYsbe6P1hKDusSbEOzGyyuce6w==",
-      "license": "MIT",
-      "bin": {
-        "marked": "bin/marked.js"
-      },
-      "engines": {
-        "node": ">= 20"
-      }
-    },
     "node_modules/merge2": {
       "version": "1.4.1",
       "resolved": "https://registry.npmmirror.com/merge2/-/merge2-1.4.1.tgz",