chore(llm): add docling service location configuration

Add configuration for routing requests to the docling-serve service
via the "/docling" endpoint, enabling access from LAN, VPN, and WAN networks.

modules/services/llm/default.nix

@@ -103,6 +103,15 @@ in
             proxyWebsockets = true;
           };
         };
+        "${cfg.backend.domain}" = {
+          locations."/docling" = {
+            host = config.services.docling-serve.host;
+            port = config.services.docling-serve.port;
+            allowLAN = true;
+            allowVPN = true;
+            allowWAN = true;
+          };
+        };
       };
     })
   ];