Move tenant dashboard routes under /dashboard/ prefix

- Update App.tsx routes to use /dashboard/ prefix for all business user routes
- Add redirect from / to /dashboard for authenticated business users
- Update Sidebar.tsx navigation links with /dashboard/ prefix
- Update SettingsLayout.tsx settings navigation paths
- Update all help pages with /dashboard/help/ routes
- Update navigate() calls in components:
  - TrialBanner, PaymentSettingsSection, NotificationDropdown
  - BusinessLayout, UpgradePrompt, QuotaWarningBanner
  - QuotaOverageModal, OpenTicketsWidget, CreatePlugin
  - MyPlugins, PluginMarketplace, HelpTicketing
  - HelpGuide, Upgrade, TrialExpired
  - CustomDomainsSettings, QuotaSettings
- Fix hardcoded lvh.me URL in BusinessEditModal to use buildSubdomainUrl

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

frontend/src/layouts/BusinessLayout.tsx

@@ -83,13 +83,13 @@ const BusinessLayoutContent: React.FC<BusinessLayoutProps> = ({ business, user,
   // Check for trial expiration and redirect
   useEffect(() => {
     // Don't check if already on trial-expired page
-    if (location.pathname === '/trial-expired') {
+    if (location.pathname === '/dashboard/trial-expired') {
       return;
     }
 
     // Redirect to trial-expired page if trial has expired
     if (business.isTrialExpired && business.status === 'Trial') {
-      navigate('/trial-expired', { replace: true });
+      navigate('/dashboard/trial-expired', { replace: true });
     }
   }, [business.isTrialExpired, business.status, location.pathname, navigate]);