[FEAT](grpc): integrate card generator service with gRPC endpoint #31

Feature description

Connect the business logic to the transport layer

What is needed to be done

• Compile .proto files to Python stubs
• Implement the gRPC Servicer method
• Map the internal Pydantic models back to gRPC response objects

Acceptance Criteria

• Sending a gRPC request returns a properly formatted gRPC response containing the generated cards