feat: add admin inventory JSON export

docs/API.md

@@ -97,6 +97,7 @@ POST   /api/v1/admin/inventory/:id/pricing/refresh
 POST   /api/v1/admin/bulk
 
 GET    /api/v1/admin/dashboard
+GET    /api/v1/admin/exports/inventory.json
 
 GET    /api/v1/admin/saved-views
 POST   /api/v1/admin/saved-views

docs/IMPLEMENTATION-STATUS.md

@@ -149,6 +149,7 @@ Remaining roadmap areas are bulk status/tag/pricing actions, richer exports/sett
 - Local development and CI can enable a deterministic fixture provider for end-to-end refresh coverage; production provider adapters remain explicitly configured deployment boundaries.
 - Pricing refresh jobs have a bounded three-attempt retry policy with exponential backoff. The worker schedules completed-job cleanup using configurable retention days and cleanup interval settings.
 - Bulk archive and asynchronous bulk pricing refresh are implemented through the seller-scoped API boundary; bulk status changes and tags remain.
+- Admin inventory JSON export is implemented at `GET /api/v1/admin/exports/inventory.json` and serializes seller-scoped admin DTOs as a downloadable attachment.
 - PostgreSQL restore verification and image snapshot restore scripts are implemented and covered by shell tests as part of the deployment drill workflow.
 - `npm audit --omit=dev` currently reports zero production vulnerabilities. Re-run the audit after dependency changes and review development-dependency findings separately before production releases.