update: bump dependencies to latest versions (#228)

Bring all outdated dependencies current: toml 1.x, sysinfo 0.39, russh 0.61 (upstream ssh-key 0.7-rc), tar 0.4.46, plus a within-semver refresh of axum/clap/tokio/tower-http/openssl/libc/rand/reqwest/serde_json/tonic*/whoami and transitive deps. No source changes required. The transitive refresh pulls rustls-webpki 0.103.13, resolving RUSTSEC-2026-0104/-0098/-0099.