feat(cli): add auth status, docker systemd probe, and version flag

[ahmedhesham6]

Description

Adds several CLI improvements: a new auth status command for credential verification, a smarter Docker preflight probe, and a --version flag.

Changes Made

• New stakpak auth status command: Shows the active profile, masked credentials, and pings the Stakpak API (/v1/account) to verify reachability and identity. Supports --profile filtering like auth list.
• Docker systemd user probe (probe_docker_user_systemd): Detects the common failure mode where usermod -aG docker $USER was run but the systemd user manager still holds stale group membership. Provides a concrete remediation command (sudo systemctl restart user@$(id -u).service).
• OS-aware Docker install remediation: Parses /etc/os-release ID field to recommend dnf on RHEL-family distros vs apt-get on Debian-family, instead of always suggesting apt-get.
• Autopilot timeout fix: Changed timeout error output from println! to eprintln! and returns Err so the caller knows the startup actually failed.
• --version flag: Adds CARGO_PKG_VERSION to the CLI struct so stakpak --version works.
• System prompt simplification: Replaces the inline Slack app manifest YAML with a pointer to stakpak autopilot channel add --help, reducing prompt size.

Testing

• All tests pass locally (cargo test --workspace)
• No clippy warnings (cargo clippy --all-targets -- -D warnings)
• Code is formatted (cargo fmt --check)
• Added unit tests for probe_docker_user_systemd (stale group, missing systemd-run, non-Linux)
• Added parse_os_release_id and docker_install_remediation with OS-specific branches

Breaking Changes

None