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.Infrastructure/Repositories/UnitOfWork.cs

@@ -60,6 +60,7 @@ public class UnitOfWork : IUnitOfWork
     private IRepository<QuoteItemPrepService>? _quoteItemPrepServices;
     private IRepository<QuoteChangeHistory>? _quoteChangeHistories;
     private IRepository<InventoryItem>? _inventoryItems;
+    private IPlainRepository<PowderCatalogItem>? _powderCatalog;
     private IInventoryTransactionRepository? _inventoryTransactions;
     private IRepository<Equipment>? _equipment;
     private IRepository<OvenCost>? _ovenCosts;
@@ -244,6 +245,10 @@ public class UnitOfWork : IUnitOfWork
     public IRepository<InventoryItem> InventoryItems =>
         _inventoryItems ??= new Repository<InventoryItem>(_context);
 
+    /// <summary>Platform-level powder catalog — no tenant filter, no soft delete.</summary>
+    public IPlainRepository<PowderCatalogItem> PowderCatalog =>
+        _powderCatalog ??= new PlainRepository<PowderCatalogItem>(_context);
+
     /// <summary>Repository for <see cref="InventoryTransaction"/> stock movements; tenant-filtered with soft delete.</summary>
     public IInventoryTransactionRepository InventoryTransactions =>
         _inventoryTransactions ??= new InventoryTransactionRepository(_context);