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/html/hints.html

@@ -134,6 +134,7 @@
           <a class="pill" href="/solutions.html">Solutions</a>
           <a class="pill" href="/service/a">Backend A</a>
           <a class="pill" href="/service/b">Backend B</a>
+          <a class="pill" href="/challenges.html#challenge-2-backend-c">Backend C (ab C2)</a>
         </div>
       </section>
 
@@ -173,6 +174,7 @@ cd certs/easyrsa
 ./easyrsa build-ca nopass
 ./easyrsa gen-req localhost nopass
 ./easyrsa sign-req server localhost</code></pre>
+            <p>Nur Runtime-Certs mounten (z. B. <code>certs/live</code>), nicht die komplette PKI.</p>
           </article>
           <article class="card">
             <h3>Fedora CA Import</h3>