pi: fix openrouter apiKey, add llama.cpp provider

openrouter was broken: !cat + nix store path is not valid omp config.
Use builtins.readFile to inline the key at eval time.

Add self-hosted llama.cpp provider at llm.sigkill.computer with
Bearer token auth.

home-manager/progs/pi.nix

@@ -18,11 +18,16 @@ let
     };
   };
 
-  # provider config — openrouter API key read from secrets at runtime
+  # provider config — secrets read at eval time via builtins.readFile
+  # (omp treats apiKey as env-var-name-or-literal, not a shell command)
   ompModels = {
     providers = {
       openrouter = {
-        apiKey = "!cat ${../secrets/openrouter_api_key}";
+        apiKey = lib.strings.trim (builtins.readFile ../secrets/openrouter_api_key);
+      };
+      "llama.cpp" = {
+        baseUrl = "https://llm.sigkill.computer";
+        apiKey = lib.strings.trim (builtins.readFile ../secrets/llama_cpp_api_key);
       };
     };
   };