fix docs: cache-control headers, Dockerfile copy order, broken links

- Add Cache-Control: no-cache on HTML responses so browser always gets
  fresh index.html (hashed asset filenames handle JS/CSS cache-busting)
- Fix Dockerfile: re-copy api/index.md after extract stage overwrites
- Revert onBrokenLinks to warn (category links unresolvable at build)
- Fix api/index.md links to use absolute /category/ paths

docs/nginx.conf

@@ -7,6 +7,7 @@ server {
 
     location / {
         try_files $uri $uri/ /index.html;
+        add_header Cache-Control "no-cache, must-revalidate";
     }
 
     location ~* \.(js|css|png|jpg|jpeg|gif|svg|ico|woff2?)$ {