hook-regex-false-positives-require-cmd-start-not-backup-anchors

The destructive-ops-blocker had two structural flaws: (1) \b word boundary matched MEMORY.md inside MEMORY.md.bak.123 because . is a non-word char, and (2) bare (rm|mv) regex matched ‘rm’ inside echo string literals. Fix: anchor with CMD_START = r’(?:^|[;&|`(]\s*)’ to require command position, and NOT_BACKUP = r’(?![.\w])’ to reject backup-suffixed filenames. Always build a 12-case test suite (real files blocked, backup allowed, string literals allowed) before deploying hook changes.