feat: support douban sync

[timerring]

Motivation

Douban (豆瓣) is a popular Chinese media and social platform widely used for book, movie, and music reviews. Adding it to the supported sync platforms allows users to publish and sync their Markdown-formatted content to Douban directly from the editor, improving coverage of mainstream Chinese media platforms.

Related Issue

N/A

Implementation

Added 'douban' to the platforms array under the 媒体平台 category in platformCategories within apps/web/src/components/editor/editor-header/PostInfo.vue.

Changed file: apps/web/src/components/editor/editor-header/PostInfo.vue

• Added 'douban' to the media platform list alongside existing platforms (wechat, toutiao, zhihu, baijiahao, wangyihao, sohu, weibo, bilibili, sspai, twitter, douyin, xiaohongshu).

Scope of Impact

• Affects the post sync platform selector in the editor header.
• No breaking changes; purely additive to the existing platform list.
• No API or behavior changes that require documentation updates.

[github-actions]

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