Remove BTCPay completely, integrate SilverPAY only, configure TeleBot with real token

- Removed all BTCPay references from services and configuration
- Implemented SilverPAY as sole payment provider (no fallback)
- Fixed JWT authentication with proper key length (256+ bits)
- Added UsersController with full CRUD operations
- Updated User model with Email and Role properties
- Configured TeleBot with real Telegram bot token
- Fixed launchSettings.json with JWT environment variable
- E2E tests passing for authentication, catalog, orders
- Payment creation pending SilverPAY server fix

🤖 Generated with Claude Code

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

LittleShop/Models/User.cs

@@ -13,8 +13,15 @@ public class User
     
     [Required]
     public string PasswordHash { get; set; } = string.Empty;
-    
+
+    [StringLength(100)]
+    public string? Email { get; set; }
+
+    [Required]
+    [StringLength(50)]
+    public string Role { get; set; } = "Staff";
+
     public DateTime CreatedAt { get; set; } = DateTime.UtcNow;
-    
+
     public bool IsActive { get; set; } = true;
 }