Add platform powder catalog, catalog-first lookup, and label scanner

- Platform PowderCatalogItem table (IPlainRepository, no tenant filter) with
  full spec fields: cure temp/time, finish, color families, clear coat flag,
  coverage sq ft/lb, transfer efficiency, IsUserContributed
- Two EF migrations: AddPowderCatalogItem + AddPowderCatalogSpecFields
- PowderCatalogController (SuperAdminOnly): import from Prismatic JSON scrape,
  Lookup AJAX endpoint (catalog-first, ranked by SKU exact match), stats view
  with Tenant Contributed card
- Unified smart Lookup button on inventory Create/Edit: catalog hit fills all
  fields via catalogSnapshot pattern; AI augments cure/finish data from product
  URL if subscription enabled; catalog miss falls through to AI lookup
- In-browser label scanner (_LabelScanModal): getUserMedia live camera feed,
  jsQR auto-detects QR codes in rAF loop; "Scan Label Text" fallback sends
  captured frame to Claude vision via /Inventory/ScanLabel
- ScanLabel endpoint handles both QR URL path (LookupByUrlAsync) and vision
  path (ScanLabelAsync); auto-inserts unrecognized products as
  IsUserContributed=true; returns wasInCatalog/addedToCatalog flags

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

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

@@ -24,6 +24,8 @@ public class InventoryItemDto
     public bool RequiresClearCoat { get; set; }
     public string? SpecPageUrl { get; set; }
     public string? ImageUrl { get; set; }
+    public string? SdsUrl { get; set; }
+    public string? TdsUrl { get; set; }
     public decimal QuantityOnHand { get; set; }
     public string UnitOfMeasure { get; set; } = "lbs";
     public decimal ReorderPoint { get; set; }
@@ -149,6 +151,14 @@ public class CreateInventoryItemDto
     [Display(Name = "Product Image URL")]
     public string? ImageUrl { get; set; }
 
+    [StringLength(1000, ErrorMessage = "URL cannot exceed 1000 characters")]
+    [Display(Name = "Safety Data Sheet URL")]
+    public string? SdsUrl { get; set; }
+
+    [StringLength(1000, ErrorMessage = "URL cannot exceed 1000 characters")]
+    [Display(Name = "Technical Data Sheet URL")]
+    public string? TdsUrl { get; set; }
+
     [Range(0, 999999999, ErrorMessage = "Quantity on hand must be 0 or greater")]
     [Display(Name = "Quantity on Hand")]
     public decimal QuantityOnHand { get; set; }