llama-cpp: add API key auth via --api-key-file

Generate and encrypt a Bearer token for llama-cpp's built-in auth.
Remove caddy_auth from the vhost since basic auth blocks Bearer-only
clients. Internal sidecars (xmrig-pause, annotations) connect
directly to localhost and are unaffected (/slots is public).

services/llama-cpp.nix

@@ -29,14 +29,18 @@
       "turbo4"
       "-fa"
       "on"
+      "--api-key-file"
+      config.age.secrets.llama-cpp-api-key.path
     ];
   };
 
   # have to do this in order to get vulkan to work
   systemd.services.llama-cpp.serviceConfig.DynamicUser = lib.mkForce false;
 
+  # Auth handled by llama-cpp --api-key-file (Bearer token).
+  # No caddy_auth — the API key is the auth layer, and caddy_auth's basic
+  # auth would block Bearer-only clients like oh-my-pi.
   services.caddy.virtualHosts."llm.${service_configs.https.domain}".extraConfig = ''
-    import ${config.age.secrets.caddy_auth.path}
     reverse_proxy :${toString config.services.llama-cpp.port}
   '';
 }