fix(llama-cpp): stage model load diagnostics

The generated gRPC source tree omitted the new header and test. Every llama.cpp-derived backend therefore failed when grpc-server.cpp included the missing header.

Assisted-by: Codex:gpt-5.6 [systematic-debugging]
Signed-off-by: Ettore Di Giacinto <mudler@localai.io>

backend/cpp/llama-cpp/prepare.sh

@@ -45,6 +45,10 @@ done
 
 cp -r CMakeLists.txt llama.cpp/tools/grpc-server/
 cp -r grpc-server.cpp llama.cpp/tools/grpc-server/
+# Model-load diagnostics (included by grpc-server.cpp) and their standalone
+# regression test.
+cp -r model_load_error.h llama.cpp/tools/grpc-server/
+cp -r model_load_error_test.cpp llama.cpp/tools/grpc-server/
 # Shared message-reconstruction helpers (included by grpc-server.cpp) and their
 # unit test (compiled only when -DLLAMA_GRPC_BUILD_TESTS=ON).
 cp -r message_content.h llama.cpp/tools/grpc-server/