docs(12-04): append self-check results to plan summary

.planning/phases/12-offer-composition-drag-drop-csv-import/12-04-SUMMARY.md

@@ -105,3 +105,17 @@ None - no external service configuration required. Pure UI change consuming Plan
 
 *Phase: 12-offer-composition-drag-drop-csv-import*
 *Completed: 2026-06-15*
+
+## Self-Check: PASSED
+
+All created/modified files verified present on disk:
+
+- FOUND: src/app/admin/offers/page.tsx
+- FOUND: src/components/admin/offers/OfferListClient.tsx
+- FOUND: .planning/phases/12-offer-composition-drag-drop-csv-import/12-04-SUMMARY.md
+
+All task commits verified present in git log:
+
+- FOUND: 68dc1b6 (Task 1)
+- FOUND: 7df4b9c (Task 2)
+- FOUND: ca37126 (docs: plan summary)