cmdValidateHealth read the phases directory four separate times for checks 6 (naming), 7 (orphaned plans), 7b (validation artifacts), and 8 (roadmap cross-reference). Hoist the directory listing into a single readdirSync call with a shared Map of per-phase file lists. Reduces syscalls from ~3N+1 to N+1 where N is the number of phase directories. Closes #1973 Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>