Implement product variant selection in TeleBot

FEATURES IMPLEMENTED:

1. Enhanced Product Display:
   - Shows multi-buy deals with pricing (e.g., "3 for £25")
   - Displays available variants grouped by type (Color, Flavor, etc.)
   - Clear visual separation between multi-buys and variants

2. Variant Selection Flow:
   - Single item: Select one variant from available options
   - Multi-buy bundles: Select individual variants for each item
   - Example: 3-pack allows choosing Red, Blue, Green individually
   - Visual feedback with checkmarks and counters

3. Smart Cart Management:
   - Tracks selected variants for each cart item
   - Supports both single variant (regular items) and multiple variants (multi-buys)
   - Unique cart entries based on product + variant combination
   - Prevents duplicate multi-buy bundles

4. User Experience Improvements:
   - Clear "Select Color/Flavor" prompts
   - Progress indicator for multi-item selection
   - Confirm button appears when selection complete
   - Clear selection option for multi-buys
   - Back navigation preserves context

TECHNICAL CHANGES:
- ProductCarouselService: Enhanced caption formatting with variants/multi-buys
- MenuBuilder: New VariantSelectionMenu with dynamic button generation
- CallbackHandler: Added handlers for selectvar, setvariant, addvariant, confirmvar
- ShoppingCart: New AddItem overload accepting Product and variant list
- CartItem: Added SelectedVariants list for multi-buy support
- UserSession: Added SelectingVariants state

This update enables customers to:
- See all available product options at a glance
- Choose specific variants when ordering
- Mix and match variants in multi-buy deals
- Get exactly what they want with clear visual feedback

Next steps: Add bot activity tracking for live dashboard

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

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

TeleBot/TeleBot/Models/ShoppingCart.cs

@@ -1,6 +1,7 @@
 using System;
 using System.Collections.Generic;
 using System.Linq;
+using LittleShop.Client.Models;
 
 namespace TeleBot.Models
 {
@@ -11,6 +12,64 @@ namespace TeleBot.Models
         public DateTime CreatedAt { get; set; } = DateTime.UtcNow;
         public DateTime UpdatedAt { get; set; } = DateTime.UtcNow;
         
+        // New method that accepts Product and variants list
+        public CartItem AddItem(Product product, int quantity = 1, Guid? multiBuyId = null, List<string>? selectedVariants = null)
+        {
+            decimal price = product.Price;
+
+            // If multi-buy selected, get the multi-buy price
+            if (multiBuyId.HasValue && product.MultiBuys != null)
+            {
+                var multiBuy = product.MultiBuys.FirstOrDefault(mb => mb.Id == multiBuyId.Value);
+                if (multiBuy != null)
+                {
+                    price = multiBuy.Price;
+                    quantity = multiBuy.Quantity; // Use the multi-buy quantity
+                }
+            }
+
+            // Create unique key for comparison
+            var variantKey = selectedVariants != null && selectedVariants.Any()
+                ? string.Join(",", selectedVariants.OrderBy(v => v))
+                : null;
+
+            // Check if item already exists
+            var existingItem = Items.FirstOrDefault(i =>
+                i.ProductId == product.Id &&
+                i.MultiBuyId == multiBuyId &&
+                (i.SelectedVariant == variantKey ||
+                 (i.SelectedVariants != null && string.Join(",", i.SelectedVariants.OrderBy(v => v)) == variantKey)));
+
+            if (existingItem != null)
+            {
+                // For multi-buys, we don't add quantities - each multi-buy is a separate bundle
+                if (!multiBuyId.HasValue)
+                {
+                    existingItem.Quantity += quantity;
+                    existingItem.UpdateTotalPrice();
+                }
+                return existingItem;
+            }
+            else
+            {
+                var newItem = new CartItem
+                {
+                    ProductId = product.Id,
+                    MultiBuyId = multiBuyId,
+                    SelectedVariant = selectedVariants?.Count == 1 ? selectedVariants[0] : null,
+                    SelectedVariants = selectedVariants ?? new List<string>(),
+                    ProductName = product.Name,
+                    UnitPrice = price,
+                    Quantity = quantity
+                };
+                newItem.UpdateTotalPrice();
+                Items.Add(newItem);
+                UpdatedAt = DateTime.UtcNow;
+                return newItem;
+            }
+        }
+
+        // Keep the old method for backward compatibility
         public void AddItem(Guid productId, string productName, decimal price, int quantity = 1, Guid? multiBuyId = null, string? selectedVariant = null)
         {
             var existingItem = Items.FirstOrDefault(i =>
@@ -96,7 +155,8 @@ namespace TeleBot.Models
     {
         public Guid ProductId { get; set; }
         public Guid? MultiBuyId { get; set; }  // For quantity pricing (e.g., 3 for £25)
-        public string? SelectedVariant { get; set; }  // For color/flavor selection
+        public string? SelectedVariant { get; set; }  // For single items - one variant
+        public List<string> SelectedVariants { get; set; } = new();  // For multi-buys - multiple variants
         public string ProductName { get; set; } = string.Empty;
         public int Quantity { get; set; }
         public decimal UnitPrice { get; set; }  // For multi-buys, this is the bundle price; for regular items, it's per-unit

TeleBot/TeleBot/Models/UserSession.cs

@@ -92,6 +92,7 @@ namespace TeleBot.Models
         BrowsingCategories,
         ViewingProducts,
         ViewingProduct,
+        SelectingVariants,
         ViewingCart,
         CheckoutFlow,
         ViewingOrders,