Redesign the documentation homepage

[intoyang]

Summary

• redesign the documentation homepage with clearer content hierarchy and navigation
• add an online demo section and a local Docker quick-start command
• improve the quick-start and topic browsing cards
• refine hover interactions, responsive layouts, and dark-mode colors

Testing

• corepack pnpm run check:ci
• corepack pnpm run build

Follow-up

This PR temporarily keeps the existing /guide/use/faq links so it can be reviewed independently. After #623 is merged, these links will be updated to /guide/faq before this PR is merged.

Screenshots

Light mode	Dark mode

[ruibaby]

点击复制按钮之后建议添加一个成功反馈。

移动端样式需要优化，会出现内容溢出导致出现滚动条。

[intoyang]

update：

• faq 链接更新为 /guide/faq。
• 为复制按钮增加成功反馈。
• 修复移动端布局的横向溢出。