feat: add package-manager distribution

[saldestechnology]

Summary

• standardize deterministic release archives and aggregate checksums
• add cargo-binstall, Homebrew, AUR, Scoop, Debian, and RPM packaging
• generate and validate package-manager metadata in CI
• prevent self-update from overwriting package-manager-owned binaries
• document release and external repository maintenance

Supported release targets

• x86_64-unknown-linux-gnu
• x86_64-apple-darwin
• aarch64-apple-darwin
• x86_64-pc-windows-msvc (no default DuckDB feature)

Linux ARM64 and musl remain unsupported because the existing CI has not established reliable builds for them.

Validation

• cargo fmt --all -- --check
• cargo clippy --workspace --all-targets -- -D warnings
• update unit tests (15 passed)
• self-update CLI tests (9 passed in focused worktree)
• package metadata generator --check, Ruby/JSON/Bash/Python syntax checks
• deterministic archive layout/checksum validation for all supported targets

Full cargo test --workspace reached 311 passing tests but failed 9 pre-existing OpenAI/Ollama provider tests on this macOS host because system-configuration attempted to create a NULL dynamic-store object. Packaging and updater tests passed. Debian/RPM construction and installation are exercised by release CI on Ubuntu.