Implement product variations, enhanced order workflow, mobile responsiveness, and product import system

## Product Variations System
- Add ProductVariation model with quantity-based pricing (1 for £10, 2 for £19, 3 for £25)
- Complete CRUD operations for product variations
- Enhanced ProductService to include variations in all queries
- Updated OrderItem to support ProductVariationId for variation-based orders
- Graceful error handling for duplicate quantity constraints
- Admin interface with variations management (Create/Edit/Delete)
- API endpoints for programmatic variation management

## Enhanced Order Workflow Management
- Redesigned OrderStatus enum with clear workflow states (Accept → Packing → Dispatched → Delivered)
- Added workflow tracking fields (AcceptedAt, PackingStartedAt, DispatchedAt, ExpectedDeliveryDate)
- User tracking for accountability (AcceptedByUser, PackedByUser, DispatchedByUser)
- Automatic delivery date calculation (dispatch date + working days, skips weekends)
- On Hold workflow for problem resolution with reason tracking
- Tab-based orders interface focused on workflow stages
- One-click workflow actions from list view

## Mobile-Responsive Design
- Responsive orders interface: tables on desktop, cards on mobile
- Touch-friendly buttons and spacing for mobile users
- Horizontal scrolling tabs with condensed labels on mobile
- Color-coded status borders for quick visual recognition
- Smart text switching based on screen size

## Product Import/Export System
- CSV import with product variations support
- Template download with examples
- Export existing products to CSV
- Detailed import results with success/error reporting
- Category name resolution (no need for GUIDs)
- Photo URLs import support

## Enhanced Dashboard
- Product variations count and metrics
- Stock alerts (low stock/out of stock warnings)
- Order workflow breakdown (pending, accepted, dispatched counts)
- Enhanced layout with more detailed information

## Technical Improvements
- Fixed form binding issues across all admin forms
- Removed external CDN dependencies for isolated deployment
- Bot Wizard form with auto-personality assignment
- Proper authentication scheme configuration (Cookie + JWT)
- Enhanced debug logging for troubleshooting

## Self-Contained Deployment
- All external CDN references replaced with local libraries
- Ready for air-gapped/isolated network deployment
- No external internet dependencies

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

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

LittleShop/Models/OrderItem.cs

@@ -11,16 +11,19 @@ public class OrderItem
     public Guid OrderId { get; set; }
     
     public Guid ProductId { get; set; }
-    
+
+    public Guid? ProductVariationId { get; set; } // Nullable for backward compatibility
+
     public int Quantity { get; set; }
-    
+
     [Column(TypeName = "decimal(18,2)")]
     public decimal UnitPrice { get; set; }
-    
+
     [Column(TypeName = "decimal(18,2)")]
     public decimal TotalPrice { get; set; }
-    
+
     // Navigation properties
     public virtual Order Order { get; set; } = null!;
     public virtual Product Product { get; set; } = null!;
+    public virtual ProductVariation? ProductVariation { get; set; }
 }