grpc-ecosystem/grpc-gateway ? reverse-engineered prompt

Build me a Go project that takes protobuf service definitions and turns them into a JSON HTTP proxy for gRPC services. I want it to follow the gRPC HTTP mapping rules, so I can expose the same backend as both gRPC and a normal REST API with simple annotations in the proto files. It should also generate OpenAPI docs, ideally Swagger 2.0 and OpenAPI 3.1 support if that fits, so the API is easy to share and test.

Please include the generator tools, the runtime pieces for the proxy, and a few clear examples that show how to wire it into a service. Make it feel like a polished open source library, with good docs, working builds, and straightforward install instructions. If you need to check current protobuf or Go guidance, look up the latest docs online.