Add interactive installer and lifecycle manager

[jacek4yang]

Summary

• add a separate Rust rust-xhttpctl binary with an interactive installation wizard
• install a dedicated unprivileged account and hardened systemd service
• support status/logs/doctor, transactional config editing, repair, verified updates, rollback, and preserve/purge uninstall
• add a version-pinned one-command bootstrap with HTTPS/SHA-256/archive-member validation
• package both binaries and the bootstrap reproducibly in v0.2.0 release assets
• add complete bilingual README installation instructions and dedicated lifecycle guides

Safety and lifecycle properties

• existing configs are backed up; invalid generated resources restore prior PEM/site content
• updates require matching daemon/manager/tag versions and preflight the installed config
• failed update/rollback activation restores the previous binary pair
• managed service runs as rust-xhttp with only CAP_NET_BIND_SERVICE
• --root ... --no-start permits installation testing without touching host /etc or systemd

Validation

• scripts/gate.sh (128 daemon tests, 7 manager tests, 3 integration tests, docs, fmt, clippy, installer smoke)
• cargo package --locked --allow-dirty
• cargo deny check
• cargo audit --no-fetch
• interactive plaintext wizard staged under an alternate root
• release/LTO build and archive extraction/install smoke
• repeated release packaging produced byte-identical archives for a fixed SOURCE_DATE_EPOCH