feat(exc): 专长交易 read-only monitoring pages

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 <[email protected]>

src/components/layout/nav.ts

@@ -1,6 +1,7 @@
 import type { LucideIcon } from 'lucide-react'
 import {
   Bot,
+  ClipboardList,
   Flag,
   FolderTree,
   Hash,
@@ -12,9 +13,12 @@ import {
   MessageSquareWarning,
   Newspaper,
   Palette,
+  Receipt,
   ScrollText,
+  Send,
   Smartphone,
   Sparkles,
+  UserCheck,
 } from 'lucide-react'
 
 export interface NavItem {
@@ -55,6 +59,15 @@ export const NAV_GROUPS: NavGroup[] = [
       },
     ],
   },
+  {
+    label: '专长交易',
+    items: [
+      { label: '需求监控', to: '/exc/demands', icon: ClipboardList },
+      { label: '派单监控', to: '/exc/dispatches', icon: Send },
+      { label: '订单监控', to: '/exc/orders', icon: Receipt },
+      { label: '服务商监控', to: '/exc/providers', icon: UserCheck },
+    ],
+  },
   {
     label: '内容审核',
     items: [