Add product image to powder inventory via AI lookup

When AI Lookup fetches a manufacturer product page, it now extracts the
og:image (Open Graph) meta tag before stripping HTML tags. The image URL
is returned in InventoryAiLookupResult.ImageUrl and automatically shown
as a preview on the Create/Edit form alongside the other filled fields.

The preview includes a Remove button to clear the image, and the Wrong
Match? button clears it along with the other AI-filled fields.

On the inventory Details page a product image card is rendered above the
Stock & Pricing card whenever ImageUrl is set. The field is nullable so
existing records and powders without an image are unaffected.

New field: InventoryItem.ImageUrl (nvarchar, nullable).
Migration: AddInventoryItemImageUrl.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/PowderCoating.Application/DTOs/Inventory/InventoryDtos.cs

@@ -23,6 +23,7 @@ public class InventoryItemDto
     public string? ColorFamilies { get; set; }
     public bool RequiresClearCoat { get; set; }
     public string? SpecPageUrl { get; set; }
+    public string? ImageUrl { get; set; }
     public decimal QuantityOnHand { get; set; }
     public string UnitOfMeasure { get; set; } = "lbs";
     public decimal ReorderPoint { get; set; }
@@ -144,6 +145,10 @@ public class CreateInventoryItemDto
     [Display(Name = "Product URL")]
     public string? SpecPageUrl { get; set; }
 
+    [StringLength(1000, ErrorMessage = "Image URL cannot exceed 1000 characters")]
+    [Display(Name = "Product Image URL")]
+    public string? ImageUrl { get; set; }
+
     [Range(0, 999999999, ErrorMessage = "Quantity on hand must be 0 or greater")]
     [Display(Name = "Quantity on Hand")]
     public decimal QuantityOnHand { get; set; }