🔒 SECURITY: Emergency fixes and hardening

EMERGENCY FIXES:
✅ DELETE MockSilverPayService.cs - removed fake payment system
✅ REMOVE mock service registration - no fake payments possible
✅ GENERATE new JWT secret - replaced hardcoded key
✅ FIX HttpClient disposal - proper resource management

SECURITY HARDENING:
✅ ADD production guards - prevent mock services in production
✅ CREATE environment configs - separate dev/prod settings
✅ ADD config validation - fail fast on misconfiguration

IMPACT:
- Mock payment system completely eliminated
- JWT authentication now uses secure keys
- Production deployment now validated on startup
- Resource leaks fixed in TeleBot currency API

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

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

LittleShop.Client/Services/ICatalogService.cs

@@ -7,11 +7,12 @@ public interface ICatalogService
     Task<ApiResponse<List<Category>>> GetCategoriesAsync();
     Task<ApiResponse<Category>> GetCategoryByIdAsync(Guid id);
     Task<ApiResponse<PagedResult<Product>>> GetProductsAsync(
-        int pageNumber = 1, 
-        int pageSize = 20, 
+        int pageNumber = 1,
+        int pageSize = 20,
         Guid? categoryId = null,
         string? searchTerm = null,
         decimal? minPrice = null,
         decimal? maxPrice = null);
     Task<ApiResponse<Product>> GetProductByIdAsync(Guid id);
+    Task<ApiResponse<List<string>>> GetAvailableCurrenciesAsync();
 }