feat: implement protobuf generation and fix Python gRPC imports

- Install and configure protobuf toolchain (protoc, protoc-gen-go, grpc-gateway)
- Successfully execute make grpc grpc-gw equivalent for api-testing project
- Generate Go protobuf files: server.pb.go, server.pb.gw.go, server_grpc.pb.go
- Generate loader and monitor protobuf files for remote testing
- Regenerate Python protobuf code: ai_extension_pb2.py, ai_extension_pb2_grpc.py
- Fix Python import paths: change absolute imports to relative imports
- Verify gRPC server functionality and service registration
- Confirm AI extension services (GenerateSQLFromNaturalLanguage, GenerateContent) are operational

Breaking changes: None
Tested: ✅ gRPC server starts successfully with all services registered

Author: KariHall619