Add Makefile to python-sdk/ with targets for common development operations:
- venv: Create virtual environment and install dependencies
- proto-gen: Generate Python gRPC code from proto files
- build: Build SDK package (wheel and sdist)
- test: Run pytest test suite
- lint: Run mypy type checking
- clean: Remove build artifacts
- help: Show available targets
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
