Fix label scanner: full field mapping, vision follow-up lookup, SDS/TDS extraction

- LookupByUrlAsync now maps all identity + spec fields from Claude response
  (manufacturer, SKU, colorName, description, sdsUrl, tdsUrl, unitCostPerLb, etc.)
  Previously only augmenting fields were mapped; Columbia QR path left 80% blank
- Vision scan follow-up: after ScanLabelAsync reads label text, automatically run
  LookupAsync using the extracted manufacturer + color/SKU to fill SDS/TDS URLs,
  product page, image, description, and any specs not printed on the bag;
  label values (cure schedule, SKU) remain authoritative and are never overwritten
- SDS/TDS URL extraction: added ExtractDocumentLinks() that scans anchor tags in
  raw HTML before tag-stripping, injects found URLs as [Structured Data] lines so
  Claude can read and echo them back in the JSON response; previously all hrefs
  were lost with the HTML stripping
- Added SdsUrl/TdsUrl to InventoryAiLookupResult, Claude system prompt JSON schema,
  LookupAsync mapping, and ScanLabel response (catalog match ?? aiResult fallback)
- SDS/TDS now also stored on auto-contributed catalog entries
- jsQR inversionAttempts: 'dontInvert' → 'attemptBoth' for better QR detection
  under varying label contrast and lighting conditions

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

src/PowderCoating.Application/Interfaces/IInventoryAiLookupService.cs

@@ -26,6 +26,8 @@ public class InventoryAiLookupResult
     public string? VendorName { get; set; }           // manufacturer/vendor name for dropdown matching
     public string? SpecPageUrl { get; set; }          // URL of the product page that was fetched
     public string? ImageUrl { get; set; }             // og:image or first product image found on the page
+    public string? SdsUrl { get; set; }               // Safety Data Sheet URL if found on product page
+    public string? TdsUrl { get; set; }               // Technical Data Sheet URL if found on product page
 
     public string? Reasoning { get; set; }       // brief explanation of what was found
 }