Auto-generate the README --help block from the CLI #41

Provide a cargo-dist-style one-line installer published as a release asset.
Because the package is pure Python (PyPI), it installs via uv, pipx, or pip
rather than downloading a binary.

Scope:

• packaging/install/canpy-installer.sh
• backend auto-detect order: uv -> pipx -> pip
• overrides: CANPY_VERSION, CANPY_NEO4J, CANPY_INSTALLER
• staged as a GitHub Release asset by release.yml