feat(local-inference): replace ollama with llama-swap + llama.cpp on zix790prors

- Add local-inference NixOS role using llama-swap (from nixpkgs-unstable)
  with llama.cpp (CUDA-enabled, from nixpkgs-unstable)
- Serves Qwen3.6-35B-A3B via HuggingFace auto-download with --cpu-moe
- Add nixosSpecialArgs for nixpkgs-unstable module access
- Configure opencode with llama-local provider pointing to zix790prors:8080
- Update gptel from Ollama backend to OpenAI-compatible llama-swap backend
- Remove ollama service from zix790prors

home/roles/base/default.nix

@@ -99,6 +99,10 @@ in
       };
     };
 
+    xdg.configFile."opencode/opencode.json" = {
+      source = ./opencode-config.json;
+    };
+
     # Note: modules must be imported at top-level home config
   };
 }