feat: add auto-generated navigation page

- Add generate-nav.sh to scan directories and build index.html
- Add nav generation step in workflow before docker build
- Replace nginx autoindex with custom nav page
- Auto-extract page title from <title> tag

nginx.conf

@@ -15,11 +15,8 @@ server {
         add_header Cache-Control "public, no-transform";
     }
 
-    # Auto-index at root for listing available pages
     location / {
-        autoindex on;
-        autoindex_exact_size off;
-        autoindex_localtime on;
+        try_files $uri $uri/ =404;
     }
 
     # Each subdirectory serves its page