delivery-checklist: Pre-Delivery Verification

In DSH development, deliverable errors stem from over-reliance on scripts. The delivery-checklist plugin ensures delivery accuracy by physically opening files for validation. Core features include checking file line counts, deduplication scanning, placeholder detection, incremental diff comparisons, and ledger logging. Its key value lies in distinguishing intra-file duplicates (defects) from inter-batch duplicates (a normal part of the funnel), preventing the shipping of defective deliverables or the accidental deletion of historical records. The plugin uses name+location as a heuristic deduplication key and must be used in conjunction with ledger maintenance upon installation.