feat(route/discord): render Markdown to HTML

[LucunJi]

• render Markdown to HTML, including Markdowns in content and embeds
  • the title extracted from content is also rendered
  • add dependencies: discord-markdown-parser, @khanacademy/simple-markdown
• improve template with
  • better spacing,
  • rendered embed fields,
  • spoiler for attachments with SPOILER_ prefix.
• misc including
  • using embed title as message title, if there is no content,
• list is not parsed cuz it's not supported in discord-markdown-parser, I may add support for it in the future
• not rigorously tested as this is not generally reviewed
• Need help: how do I get correct timezone for parsing timestamp without using user's IP?

Involved Issue / 该 PR 相关 Issue

N/A

Example for the Proposed Route(s) / 路由地址示例

(it should fail without proper DISCORD_AUTHORIZATION)

/discord/channel/0

New RSS Route Checklist / 新 RSS 路由检查表

• New Route / 新的路由
  • Follows Script Standard / 跟随 路由规范
• Anti-bot or rate limit / 反爬/频率限制
  • If yes, do your code reflect this sign? / 如果有, 是否有对应的措施?
• Date and time / 日期和时间
  • Parsed / 可以解析
  • Correct time zone / 时区正确
• New package added / 添加了新的包
• Puppeteer

Note / 说明

[github-actions]

Successfully generated as following:

http://localhost:1200/discord/channel/0 - Failed ❌

HTTPError: Response code 503 (Service Unavailable)

Error Message:<br/>ConfigNotFoundError: Discord RSS is disabled due to the lack of &lt;a href=&quot;https://docs.rsshub.app/deploy/config#route-specific-configurations&quot;&gt;relevant config&lt;/a&gt;
Route: /discord/channel/:channelId
Full Route: /discord/channel/0
Node Version: v22.17.1
Git Hash: 8267ce77

[github-actions]

Successfully generated as following:

http://localhost:1200/discord/channel/0 - Failed ❌

HTTPError: Response code 503 (Service Unavailable)

Error Message:<br/>ConfigNotFoundError: Discord RSS is disabled due to the lack of &lt;a href=&quot;https://docs.rsshub.app/deploy/config#route-specific-configurations&quot;&gt;relevant config&lt;/a&gt;
Route: /discord/channel/:channelId
Full Route: /discord/channel/0
Node Version: v22.17.1
Git Hash: 6fff21ce

[TonyRL]

This may causes the title to include HTML. title is expected to have plain text only.

[github-actions]

Successfully generated as following:

http://localhost:1200/discord/channel/0 - Failed ❌

HTTPError: Response code 503 (Service Unavailable)

Error Message:<br/>ConfigNotFoundError: Discord RSS is disabled due to the lack of &lt;a href=&quot;https://docs.rsshub.app/deploy/config#route-specific-configurations&quot;&gt;relevant config&lt;/a&gt;
Route: /discord/channel/:channelId
Full Route: /discord/channel/0
Node Version: v22.17.1
Git Hash: cae858a5