Fix broken relative links in cookbook docs (Fix #2490)

Cookbook body links referenced sibling pages with a bare slug
(e.g. `c14-keep-alive`). Under the pretty-URL layout each page lives
in its own directory, so these resolve against the page's own
directory and 404. Prefix them with `../` to match the convention
already used in the tour and llm-app sections.

Verified clean with `docs-gen check`.

docs-src/pages/en/cookbook/t03-ssl-server.md

@@ -34,7 +34,7 @@ httplib::SSLServer svr("cert.pem", "key.pem",
                        nullptr, nullptr, "password");
 ```
 
-The third and fourth arguments are for client certificate verification (mTLS, see [T04. Configure mTLS](t04-mtls)). For now, pass `nullptr`.
+The third and fourth arguments are for client certificate verification (mTLS, see [T04. Configure mTLS](../t04-mtls)). For now, pass `nullptr`.
 
 ## Load PEM data from memory
 
@@ -73,6 +73,6 @@ openssl req -x509 -newkey rsa:2048 -days 365 -nodes \
 
 In production, use certificates from Let's Encrypt or your internal CA.
 
-> **Warning:** Binding an HTTPS server to port 443 requires root. For a safe way to do that, see the privilege-drop pattern in [S18. Control startup order with `listen_after_bind`](s18-listen-after-bind).
+> **Warning:** Binding an HTTPS server to port 443 requires root. For a safe way to do that, see the privilege-drop pattern in [S18. Control startup order with `listen_after_bind`](../s18-listen-after-bind).
 
-> For mutual TLS (client certificates), see [T04. Configure mTLS](t04-mtls).
+> For mutual TLS (client certificates), see [T04. Configure mTLS](../t04-mtls).