Migrate InvoiceService to dependency injection pattern

- Add INVOICE_SERVICE token to DI container
- Register InvoiceService in base module with proper lifecycle
- Update market store to use dependency injection instead of singleton
- Remove exported singleton from InvoiceService class
- Add comprehensive migration documentation with examples
- Maintain type safety with proper TypeScript interfaces

This migration eliminates the legacy singleton pattern and improves:
- Testability through service injection
- Modular architecture with clear boundaries
- Single source of truth for service instances
- Consistent dependency injection patterns

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

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

src/core/di-container.ts

@@ -134,6 +134,9 @@ export const SERVICE_TOKENS = {
   
   // Events services
   EVENTS_SERVICE: Symbol('eventsService'),
+  
+  // Invoice services
+  INVOICE_SERVICE: Symbol('invoiceService'),
 } as const
 
 // Type-safe injection helpers