Lazily enrich catalog specs from TDS on first use

Specific gravity, coverage, and ~55% of cure specs aren't in the Columbia feed.
Rather than read 2,400 TDS PDFs up front, enrich a catalog item the first time
it's actually used:

- FetchTdsCureSpecsAsync now also extracts specific gravity from the TDS.
- New EnsureCatalogTdsSpecsAsync fills a catalog item's specific gravity (and
  any missing cure temp/time) from its TDS, then derives theoretical coverage
  (192.3 / (SG x mils)). No-op once specific gravity is known or when there's no
  TDS; persists to the catalog so the work is done once and benefits everyone.
- Hooked into the catalog->inventory paths (CreateIncomingFromCatalog, the
  custom-powder receive enrichment, and ReceivePowderFromCatalog) so a powder's
  full specs land on both the catalog and the new inventory record. DashboardController
  gains the AI lookup service for this.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/PowderCoating.Web/Controllers/InventoryController.cs

@@ -1263,6 +1263,10 @@ public class InventoryController : Controller
             if (catalogItem == null)
                 return Json(new { success = false, error = "Catalog item not found." });
 
+            // First use of this powder — lazily fill specific gravity / cure from its TDS so the new
+            // inventory record (and the catalog) carry complete specs. No-op once already enriched.
+            await _aiLookupService.EnsureCatalogTdsSpecsAsync(catalogItem);
+
             var companyId = _tenantContext.GetCurrentCompanyId() ?? 0;
 
             // Find the default coating category to assign.