feat: product website for GitHub Pages + author CodingPlan.Site

- website/: zero-dependency static landing page (HTML+CSS), corporate
  light theme, real app screenshots, download links pointing to the
  git.codingplan.site release channel (exe/msi) with GitHub mirror
- .github/workflows/deploy-website.yml: deploy website/ to GitHub Pages
  on push to main (paths: website/**)
- package.json: author -> CodingPlan.Site
- README: link to the site and its source folder

README.md

@@ -2,6 +2,8 @@
 
 开源的现代化终端应用：本地终端 + SSH 远程会话 + 分屏管理 + 主题/字体定制。Electron + React + TypeScript，从 0 到 1 独立开发。
 
+> 产品官网（GitHub Pages）：<https://billowliu2.github.io/OpenTerminal/>，源码在 [`website/`](website/)。
+
 ## 快速开始
 
 ```bash