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/Areas/Admin/Controllers/ActivityController.cs

@@ -0,0 +1,55 @@
+using Microsoft.AspNetCore.Authorization;
+using Microsoft.AspNetCore.Mvc;
+using LittleShop.Services;
+
+namespace LittleShop.Areas.Admin.Controllers;
+
+[Area("Admin")]
+[Authorize(Policy = "AdminOnly")]
+public class ActivityController : Controller
+{
+    private readonly IBotActivityService _activityService;
+    private readonly ILogger<ActivityController> _logger;
+
+    public ActivityController(IBotActivityService activityService, ILogger<ActivityController> logger)
+    {
+        _activityService = activityService;
+        _logger = logger;
+    }
+
+    // GET: /Admin/Activity
+    public IActionResult Index()
+    {
+        return View();
+    }
+
+    // GET: /Admin/Activity/Live
+    public IActionResult Live()
+    {
+        return View();
+    }
+
+    // API endpoint for initial data load
+    [HttpGet]
+    public async Task<IActionResult> GetSummary()
+    {
+        var summary = await _activityService.GetLiveActivitySummaryAsync();
+        return Json(summary);
+    }
+
+    // API endpoint for activity stats
+    [HttpGet]
+    public async Task<IActionResult> GetStats(int hoursBack = 24)
+    {
+        var stats = await _activityService.GetActivityTypeStatsAsync(hoursBack);
+        return Json(stats);
+    }
+
+    // API endpoint for recent activities
+    [HttpGet]
+    public async Task<IActionResult> GetRecent(int minutesBack = 5)
+    {
+        var activities = await _activityService.GetRecentActivitiesAsync(minutesBack);
+        return Json(activities);
+    }
+}