Improve workshop consistency and navigation

Align challenge numbering and cross-page links, and clarify Backend C/TLS guidance so participants always see valid routes and safer cert mounting defaults.

proxy/nginx.tls.example.conf

@@ -34,8 +34,8 @@ http {
     listen 443 ssl;
     server_name localhost;
 
-    ssl_certificate /etc/nginx/pki/issued/localhost.crt;
-    ssl_certificate_key /etc/nginx/pki/private/localhost.key;
+    ssl_certificate /etc/nginx/certs/localhost.crt;
+    ssl_certificate_key /etc/nginx/certs/localhost.key;
     ssl_protocols TLSv1.2 TLSv1.3;
     ssl_prefer_server_ciphers on;