New nav group with four pages against the Exc admin API: - /exc/demands — status/mode filters, detail sheet with related services, quotes and dispatch rounds - /exc/dispatches — status/round filters - /exc/orders — status/payment filters, detail sheet with items and 状态流转 audit trail - /exc/providers — status/verified filters, detail sheet with dispatch settings and status logs Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>