Sweep the remaining call sites onto the one target-root convention

[sameera]

Finish the repo-wide sweep story #280 deliberately deferred: migrate the five remaining call
sites still on a prior root-resolution convention — record_digest.ts (--dir flag),
close_migration.ts (positional-or-cwd), validate-concepts.ts / derive-entry-diff.ts /
get_abs_doc_path.ts (bare process.cwd(), no override) — onto takeTargetRoot /
_find_config_root, so epic #248's success metric ("zero call sites remain on any of the six
prior conventions") is fully met rather than partially.

Meta

• feature: docs/features/component-distribution
• estimate: S
• source: deferred from epic Reach project state through an explicitly passed target root (Reach project state through an explicitly passed target root #248) (2026-08-25)