Implement product multi-buys and variants system

Major restructuring of product variations:
- Renamed ProductVariation to ProductMultiBuy for quantity-based pricing (e.g., "3 for £25")
- Added new ProductVariant model for string-based options (colors, flavors)
- Complete separation of multi-buy pricing from variant selection

Features implemented:
- Multi-buy deals with automatic price-per-unit calculation
- Product variants for colors/flavors/sizes with stock tracking
- TeleBot checkout supports both multi-buys and variant selection
- Shopping cart correctly calculates multi-buy bundle prices
- Order system tracks selected variants and multi-buy choices
- Real-time bot activity monitoring with SignalR
- Public bot directory page with QR codes for Telegram launch
- Admin dashboard shows multi-buy and variant metrics

Technical changes:
- Updated all DTOs, services, and controllers
- Fixed cart total calculation for multi-buy bundles
- Comprehensive test coverage for new functionality
- All existing tests passing with new features

Database changes:
- Migrated ProductVariations to ProductMultiBuys
- Added ProductVariants table
- Updated OrderItems to track variants

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

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

LittleShop/DTOs/BotActivityDto.cs

@@ -0,0 +1,82 @@
+using System.ComponentModel.DataAnnotations;
+
+namespace LittleShop.DTOs;
+
+public class BotActivityDto
+{
+    public Guid Id { get; set; }
+    public Guid BotId { get; set; }
+    public string BotName { get; set; } = string.Empty;
+    public string SessionIdentifier { get; set; } = string.Empty;
+    public string UserDisplayName { get; set; } = string.Empty;
+    public string ActivityType { get; set; } = string.Empty;
+    public string ActivityDescription { get; set; } = string.Empty;
+    public Guid? ProductId { get; set; }
+    public string ProductName { get; set; } = string.Empty;
+    public Guid? OrderId { get; set; }
+    public string CategoryName { get; set; } = string.Empty;
+    public decimal? Value { get; set; }
+    public int? Quantity { get; set; }
+    public string Platform { get; set; } = "Telegram";
+    public string DeviceType { get; set; } = string.Empty;
+    public string Location { get; set; } = string.Empty;
+    public DateTime Timestamp { get; set; }
+    public string Metadata { get; set; } = "{}";
+}
+
+public class CreateBotActivityDto
+{
+    [Required]
+    public Guid BotId { get; set; }
+
+    [Required]
+    [StringLength(256)]
+    public string SessionIdentifier { get; set; } = string.Empty;
+
+    [StringLength(100)]
+    public string UserDisplayName { get; set; } = string.Empty;
+
+    [Required]
+    [StringLength(50)]
+    public string ActivityType { get; set; } = string.Empty;
+
+    [Required]
+    [StringLength(500)]
+    public string ActivityDescription { get; set; } = string.Empty;
+
+    public Guid? ProductId { get; set; }
+
+    [StringLength(200)]
+    public string ProductName { get; set; } = string.Empty;
+
+    public Guid? OrderId { get; set; }
+
+    [StringLength(100)]
+    public string CategoryName { get; set; } = string.Empty;
+
+    public decimal? Value { get; set; }
+
+    public int? Quantity { get; set; }
+
+    [StringLength(100)]
+    public string Platform { get; set; } = "Telegram";
+
+    [StringLength(50)]
+    public string DeviceType { get; set; } = string.Empty;
+
+    [StringLength(100)]
+    public string Location { get; set; } = string.Empty;
+
+    public string Metadata { get; set; } = "{}";
+}
+
+public class LiveActivitySummaryDto
+{
+    public int ActiveUsers { get; set; }
+    public int TotalActivitiesLast5Min { get; set; }
+    public int ProductViewsLast5Min { get; set; }
+    public int CartsActiveNow { get; set; }
+    public decimal TotalValueInCartsNow { get; set; }
+    public List<string> ActiveUserNames { get; set; } = new();
+    public List<BotActivityDto> RecentActivities { get; set; } = new();
+}