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.Application/Interfaces/IInventoryAiLookupService.cs

@@ -54,4 +54,11 @@ public interface IInventoryAiLookupService
     /// using Claude vision. Used by the in-browser label scanner.
     /// </summary>
     Task<InventoryAiLookupResult> ScanLabelAsync(string base64Image, string mediaType);
+
+    /// <summary>
+    /// Fetches a Technical Data Sheet URL and extracts cure temperature and cure time.
+    /// Called when the main lookup found a TDS URL but cure specs are still missing.
+    /// Returns Success=false silently (no UI error) when the TDS is a PDF or unreachable.
+    /// </summary>
+    Task<InventoryAiLookupResult> FetchTdsCureSpecsAsync(string tdsUrl, string? colorName);
 }