Prepare and serve verified Business item rankings

[sridharkalaibala]

Returned invoices replace their current item list, which made historical best-selling item figures unprovable. This change preserves bounded original item facts with the first return, allocates recorded invoice/refund amounts exactly, and prepares a top-20 branch/day ranking on the reporting desktop. Missing or contradictory history suppresses the ranking instead of presenting partial figures as complete.

The /business/v1/items endpoint requires live financial and item access, accepts one authorized branch, and reads only fenced prepared snapshots. Discovery and desktop/Gateway capability negotiation preserve older overview clients. Item quantities remain separate by unit; revenue includes recorded discounts, tax and rounding and is not profit.

Validation: 131 related unit/repository tests and 30 real-Mongo integration tests pass, including the actual return writer, sync transport, desktop worker/agent/Gateway publication, bounded read path, live ACL removal and Community recovery. Targeted lint, formatting, attribution and generated-doc checks pass. OpenAPI validates with 14 existing ambiguous-path warnings.

Stacked on PR #1015. Companion changes are on codex/business-item-insights in Gateway and posnic-business. This remains a draft: complete-source qualification, physical-device checks and wider release gates remain open. No CI workflow changes.

[sridharkalaibala]

The complete Business companion stack, including this change, is integrated into develop through #1023. All checks, including CodeQL, passed before merge. Closing this superseded stacked PR.