refactor(docs): consolidate stage-0 into stage-1 and update routing

- Update homepage links in zh-cn and zh-tw to point to stage-1
- Update internal navigation links within stage-1 index files
- Remove obsolete github-pages-deployment document
- Update sitemap generation script to reflect stage-0 removal

docs/ja-jp/index.md

@@ -17,10 +17,10 @@ hero:
   actions:
     - theme: brand
       text: 一緒にvibeを始めよう！
-      link: /ja-jp/stage-0/
+      link: /ja-jp/stage-1/
     - theme: alt
       text: コース概要
-      link: /ja-jp/stage-0/
+      link: /ja-jp/stage-1/
 ---
 
 <HomeFeatures />