Fixed two issues preventing wheel builds from succeeding:

1. **sdist path error**: Maturin doesn't allow paths with '..' in sdist
   archives. Copied README.md to package directory and updated
   pyproject.toml to use local README.md instead of ../../README.md

2. **manylinux Python interpreter error**: When using manylinux Docker
   container, actions/setup-python sets up Python on the host, but
   maturin can't access it inside the container. Removed setup-python
   step for Linux builds and use -i python$VERSION to specify which
   Python interpreter to use inside the manylinux container.

Changes:
- Copy README.md to packages/colcon-cargo-ros2/
- Update pyproject.toml: readme = "README.md" (was "../../README.md")
- Remove actions/setup-python from Linux job (not needed with manylinux)
- Add -i python$VERSION to maturin args for Linux builds

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>