P19b — comparison and reconciliation user guide

Base 5d6082f, isolated docs-graph-reconciliation. Update the existing docs/web-ui-search/investigations.md; no new product page or route. Read CLAUDE.md. Product authorities: backend 6eaf9b6, its brief/DTO 4078daa and d2bdaed, frontend 932c8194 and its brief 8254d201.

Explain staff-only historical comparison as read-only, explicit current-to-team- evidence loading, personal proof exclusion, no search/credits, per-operation accept/ignore/unchanged, explicit dependencies, preview and final confirmation. Cover new internal items, blocked manual/excluded/retired targets, atomic application, conflicts/unknown outcomes and preserved choices without automatic retry. Replace the old blanket statement that comparison/reconciliation are unavailable; retain an explicit statement that historical reconciliation remains unavailable.

All guide/report Markdown must be finalized before the final Docusaurus build and typecheck. Check generated anchors and local links, not an assumed page count. Root quality + frontend conformity precede coordinator publication after compatible backend/frontend deployment. No push or principal edits.