feat(admin): add /api/import/bypos endpoint for bypos-collector import

Brings the bypos JSONL import backend (handler + store) into main so the
bypos-collector tool's import feature works end-to-end. Records are upserted
on GTIN with manufacturer/MSRP/barcode/source provenance, quality recomputed
per product. Only status=hit records with a name are imported.

Co-Authored-By: Devin AI <158243242+devin-ai-integration[bot]@users.noreply.github.com>

api/internal/adminhandler/handler.go

@@ -90,6 +90,8 @@ func (h *Handler) Router() http.Handler {
 			r.Put("/api/categories/{id}", h.UpdateCategory)
 			r.Delete("/api/categories/{id}", h.DeleteCategory)
 
+			r.Post("/api/import/bypos", h.ImportBypos)
+
 			r.Get("/api/submissions", h.ListSubmissions)
 			r.Get("/api/submissions/{id}", h.GetSubmission)
 			r.Post("/api/submissions/{id}/approve", h.ApproveSubmission)