feat: Phase 7 frontend - Refund/Reconciliation core + Payments & Finance section

New core/finance (Refund/ReconciliationRecord/Settlement models + gateway/
token, mock backed, seeded empty) and features/admin/finance (facade +
page: reconciliation queue with resolve action, settlements placeholder).
New /backoffice/finance route + nav entry, nav i18n key in all 3 languages.
Against docs/backend/PHASE-7-PAYMENTS-RECONCILIATION-CONTRACT.md.

Note: does not wire AdminOrdersLocalGateway's existing mock
requestRefund(id) method into this new Refund flow yet - that's a small
follow-up once Phase 2's real Order backend exists to refund against.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

src/app/i18n/translations.ts

@@ -2070,6 +2070,7 @@ export interface Translations {
       moderation: string;
       notifications: string;
       integrations: string;
+      finance: string;
       reports: string;
       partnersGroup: string;
       sellerManagement: string;