feat(analytics): Umami integration with per-port admin settings

Adds /[portSlug]/website-analytics dashboard page (pageviews, top
pages, top referrers) and a per-port admin config UI for the
Umami URL / website-ID / API token. Settings live in system_settings
keyed per-port so a future second port has its own Umami account.
Adds a website glance tile to the main dashboard, a server-side
test-credentials endpoint, and a stable cache key for the active-
visitor poll so React Query doesn't fragment the cache per range.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/app/(dashboard)/[portSlug]/admin/page.tsx

@@ -18,6 +18,7 @@ import {
   Users,
   UsersRound,
   Webhook,
+  Globe,
 } from 'lucide-react';
 
 import { Card, CardContent, CardDescription, CardHeader, CardTitle } from '@/components/ui/card';
@@ -209,6 +210,12 @@ const GROUPS: AdminGroup[] = [
         description: 'Configure the AI provider used by the mobile receipt scanner.',
         icon: ScrollText,
       },
+      {
+        href: 'website-analytics',
+        label: 'Website analytics (Umami)',
+        description: 'Per-port Umami URL, API token, and Website ID.',
+        icon: Globe,
+      },
     ],
   },
 ];