feat(i18n): Comprehensive internationalization of frontend components and pages

Translate all hardcoded English strings to use i18n translation keys:

Components:
- TransactionDetailModal: payment details, refunds, technical info
- ConnectOnboarding/ConnectOnboardingEmbed: Stripe Connect setup
- StripeApiKeysForm: API key management
- DomainPurchase: domain registration flow
- Sidebar: navigation labels
- Schedule/Sidebar, PendingSidebar: scheduler UI
- MasqueradeBanner: masquerade status
- Dashboard widgets: metrics, capacity, customers, tickets
- Marketing: PricingTable, PluginShowcase, BenefitsSection
- ConfirmationModal, ServiceList: common UI

Pages:
- Staff: invitation flow, role management
- Customers: form placeholders
- Payments: transactions, payouts, billing
- BookingSettings: URL and redirect configuration
- TrialExpired: upgrade prompts and features
- PlatformSettings, PlatformBusinesses: admin UI
- HelpApiDocs: API documentation

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

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

frontend/src/hooks/usePlatform.ts

@@ -10,6 +10,7 @@ import {
   getBusinessUsers,
   updateBusiness,
   createBusiness,
+  deleteBusiness,
   PlatformBusinessUpdate,
   PlatformBusinessCreate,
   getTenantInvitations,
@@ -87,6 +88,21 @@ export const useCreateBusiness = () => {
   });
 };
 
+/**
+ * Hook to delete a business/tenant (platform admin only)
+ */
+export const useDeleteBusiness = () => {
+  const queryClient = useQueryClient();
+
+  return useMutation({
+    mutationFn: (businessId: number) => deleteBusiness(businessId),
+    onSuccess: () => {
+      // Invalidate and refetch businesses list
+      queryClient.invalidateQueries({ queryKey: ['platform', 'businesses'] });
+    },
+  });
+};
+
 // ============================================================================
 // Tenant Invitation Hooks
 // ============================================================================