Generate shell completions and manual assets

[konojunya]

Summary

• add deterministic stack completions <bash|zsh|fish> and stack manpage commands backed by audited command metadata
• package exact completion and manual files in every release archive and validate binary, archive, help, and metadata drift
• document Homebrew, Aqua, direct-install, and future Cargo ownership boundaries and prepare the v0.4.0 release contract

Verification

• cargo +stable fmt --check
• cargo +stable test --locked
• pinned specification formatter and template conformance suites
• cargo +stable clippy --all-targets --all-features --locked -- -D warnings
• RUSTDOCFLAGS="-D warnings" cargo +stable doc --no-deps --locked
• cargo +1.85.0 test --locked
• cargo +1.85.0 clippy --all-targets --all-features --locked -- -D warnings
• cargo +stable llvm-cov --all-features --locked --fail-under-lines 90 --fail-under-functions 95 --fail-under-regions 90 (90.24% lines, 97.39% functions, 91.04% regions)
• JavaScript distribution and release-policy validators (53 tests)
• Python generation, normalization, and packaging suite (12 tests)
• bash top-level and nested completion smoke; zsh syntax; roff rendering
• reproducible-release path smoke for a normalized, ad-hoc-signed aarch64 macOS 13 binary and nine-entry v0.4.0 archive