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

package.json

@@ -4,7 +4,7 @@
   "version": "1.0.15",
   "description": "Open-source terminal with SSH, split panes, themes and fonts",
   "main": "out/main/index.js",
-  "author": "Bill",
+  "author": "CodingPlan.Site",
   "license": "MIT",
   "private": true,
   "scripts": {