feat(app): unified demo mode + public-demo build for Vercel

- Central demo-mode helper (lib/demo-mode.ts): ?demo=1 query flag plus
  VITE_PUBLIC_DEMO build flag that makes every route demo for the
  public Vercel showcase.
- Single demo fixture source (lib/demo-data.ts): projects, services,
  builds, databases, cron, HA, security, host monitoring, templates.
  Fixes cross-page ID drift that broke project navigation.
- Demo support on Projects, HA, Security, Usage, Templates, Landing,
  Service detail; DemoRestricted gate on People/Settings/Audit/Admin.
- Demo-aware PlatformShell: nav filtering, env:demo, demo account menu,
  ?demo=1 preserved through internal links.
- TemplatesPage: selection moved into ?template= URL param for deep
  links; template fixtures shared via demo-data.
- requestJson returns {} for unparseable 200 bodies (SPA fallback) so
  envelope unwraps degrade instead of dereferencing null.
- Recharts ResponsiveContainer initialDimension kills -1 warnings.
- vercel.json: vite framework + SPA rewrites for direct deep links.

Generated with [Devin](https://devin.ai)

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

app/frontend/src/features/audit/pages/AuditLogsPage.tsx

@@ -1,7 +1,9 @@
 import { useDeferredValue, useState } from 'react';
 import { useQuery } from '@tanstack/react-query';
 import { listAuditLogs } from '@/lib/api-client';
+import { useDemoMode } from '@/lib/demo-mode';
 import { formatDate, formatRelative } from '@/lib/time';
+import { DemoRestricted } from '@/shared/components';
 import { ScrollText, ChevronLeft, ChevronRight, Loader2 } from 'lucide-react';
 
 const PAGE_SIZE = 50;
@@ -17,6 +19,7 @@ const inputClass =
   'h-9 px-3 rounded-[var(--radius-md)] border border-[var(--border-subtle)] bg-[var(--surface-muted)] text-sm text-[var(--text-primary)] placeholder:text-[var(--text-muted)] focus:border-[var(--accent-primary)] focus:ring-1 focus:ring-[var(--accent-primary)] transition-all';
 
 export function AuditLogsPage() {
+  const isDemoMode = useDemoMode();
   const [resource, setResource] = useState('');
   const [action, setAction] = useState('');
   const [actor, setActor] = useState('');
@@ -42,8 +45,13 @@ export function AuditLogsPage() {
       const since = option && 'ms' in option ? new Date(Date.now() - option.ms).toISOString() : undefined;
       return listAuditLogs({ ...filters, since });
     },
+    enabled: !isDemoMode,
   });
 
+  if (isDemoMode) {
+    return <DemoRestricted feature="Audit logs" />;
+  }
+
   const logs = logsQuery.data ?? [];
   const hasNext = logs.length === PAGE_SIZE;
   const hasFilters = Boolean(resource || action || actor || range);