lidarr_missing_art.sh's album-directory-map loop (both the cache-hit and
live-fallback branches) and arr_profile_enforcer.sh's _is_kids_path()
called dirname/basename once per item -- 127K+ tracks and ~4000
series/movies respectively, each call forking a subprocess. Measured:
0.39s vs 72.2s for 20K calls, ~185x. Verified identical output against
real paths (including unicode/space/paren edge cases) before switching.