fix(zsh-plugin): remove debug logs, fix chpwd recursion, require coreutils

- Strip all debug print statements; clean single-prompt output - Re-entry guard (_MUSE_REFRESHING) on _muse_hook_chpwd prevents the infinite recursion that fired when cd inside the dirty-check subshell triggered chpwd_functions (subshells inherit parent variables) - Revert env -C back to cd — env -C broke muse discovery (rc=127) because it spawns a plain process outside ZSH's venv/PATH activation - timeout (GNU coreutils) is now an explicit dependency; install via brew