Fall back to TDS sheet for cure specs when main lookup returns none

After the main AI lookup and catalog search, if CureTemperatureF or
CureTimeMinutes is still null but a TDS URL was found, fetch that page
and ask Claude to extract just the cure schedule.

- IInventoryAiLookupService.FetchTdsCureSpecsAsync: new interface method
- InventoryAiLookupService.FetchTdsCureSpecsAsync: fetches the TDS URL via
  the existing FetchPageAsync pipeline (JSON-LD + doc-link extraction, HTML
  stripping). If the page is a PDF or unreachable, returns Success=false
  silently so no error surfaces in the UI. Otherwise sends a small targeted
  prompt that asks only for cureTemperatureF and cureTimeMinutes and uses
  MaxTokens=256 so the call is fast and cheap.
- InventoryController.ScanLabel: after catalog lookup, computes the resolved
  cure values (catalog preferred over AI result). If either is null and a
  TDS URL exists, calls FetchTdsCureSpecsAsync and merges any newly found
  values back into aiResult before building the JSON response.

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

src/PowderCoating.Web/Controllers/InventoryController.cs

@@ -834,6 +834,23 @@ public class InventoryController : Controller
             }
         }
 
+        // If cure specs are still missing but we have a TDS URL, fetch it and try to extract
+        // cure temperature and cure time. Most TDS pages are HTML; PDFs fail silently.
+        var resolvedCureTemp = catalogMatch?.CureTemperatureF ?? aiResult.CureTemperatureF;
+        var resolvedCureTime = catalogMatch?.CureTimeMinutes  ?? aiResult.CureTimeMinutes;
+        var resolvedTdsUrl   = catalogMatch?.TdsUrl ?? aiResult.TdsUrl;
+
+        if ((resolvedCureTemp == null || resolvedCureTime == null) && !string.IsNullOrEmpty(resolvedTdsUrl))
+        {
+            _logger.LogInformation("Cure specs missing after main lookup; trying TDS at {Url}", resolvedTdsUrl);
+            var tdsResult = await _aiLookupService.FetchTdsCureSpecsAsync(resolvedTdsUrl, colorName);
+            if (tdsResult.Success)
+            {
+                if (resolvedCureTemp == null) aiResult.CureTemperatureF = tdsResult.CureTemperatureF;
+                if (resolvedCureTime == null) aiResult.CureTimeMinutes  = tdsResult.CureTimeMinutes;
+            }
+        }
+
         // Check if this product already exists in the tenant's inventory.
         // Match by ManufacturerPartNumber first (most precise); fall back to color name + manufacturer.
         // Returns the first active match so the UI can prompt to add stock inline.