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/components/NotificationDropdown.tsx

@@ -59,7 +59,7 @@ const NotificationDropdown: React.FC<NotificationDropdownProps> = ({ variant = '
     // Handle time-off request notifications - navigate to time blocks page
     // Includes both new requests and modified requests that need re-approval
     if (notification.data?.type === 'time_off_request' || notification.data?.type === 'time_off_request_modified') {
-      navigate('/time-blocks');
+      navigate('/dashboard/time-blocks');
       setIsOpen(false);
       return;
     }
@@ -224,7 +224,7 @@ const NotificationDropdown: React.FC<NotificationDropdownProps> = ({ variant = '
               </button>
               <button
                 onClick={() => {
-                  navigate('/notifications');
+                  navigate('/dashboard/notifications');
                   setIsOpen(false);
                 }}
                 className="text-xs text-brand-600 hover:text-brand-700 dark:text-brand-400 font-medium"