fix(erp-export): strict seit format, DB clock for settle window, movement index, one scope per key

Co-Authored-By: Claude Opus 5.5 (1M context) <[email protected]>

ApiCore-Backend/prisma/migrations/20261013130000_batch_movement_created_at_index/migration.sql

@@ -0,0 +1,3 @@
+-- ERP-Export /bewegungen sortiert und blättert nach (createdAt, id).
+-- CreateIndex
+CREATE INDEX "BatchMovement_createdAt_id_idx" ON "BatchMovement"("createdAt", "id");