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/api/platform.ts

@@ -116,6 +116,14 @@ export const createBusiness = async (
   return response.data;
 };
 
+/**
+ * Delete a business/tenant (platform admin only)
+ * This permanently deletes the tenant and all associated data
+ */
+export const deleteBusiness = async (businessId: number): Promise<void> => {
+  await apiClient.delete(`/platform/businesses/${businessId}/`);
+};
+
 /**
  * Get all users (platform admin only)
  */