To avoid version collisions with upstream

compgen is a bash builtin that requires programmable completion support
to be compiled in. Nix-provided bash builds (e.g. bash 5.3 from
nixpkgs) strip programmable completion, so compgen is not available as
a builtin and fails with 'command not found'. The 2>/dev/null in
_list_plugins silently swallowed this error, causing the Plugins
section in help output to be empty.

Replace compgen -c with _find_path_commands(), which scans PATH
directories directly using glob matching. This works on any bash
regardless of compile-time feature flags.

find -printf is a GNU extension not available in macOS BSD find. On bare
macOS (outside devenv which provides GNU coreutils), the command fails
silently due to 2>/dev/null, causing cmd_closed to return no output.

Replace with ls -t which is POSIX and works on both GNU and BSD systems.
SC2012 is suppressed since ticket IDs are always alphanumeric.