Fix QR label modal: allow self in frame-src CSP, fix Bootstrap API call

frame-src was missing 'self' so the Label iframe was blocked by CSP.
bootstrap.Modal.getOrCreate does not exist; correct method is getOrCreateInstance.

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

src/PowderCoating.Web/Views/Inventory/Index.cshtml

@@ -519,7 +519,7 @@
             e.stopPropagation();
             const frame = document.getElementById('qrLabelFrame');
             frame.src = '@Url.Action("Label", "Inventory")/' + itemId + '?embed=true';
-            bootstrap.Modal.getOrCreate(document.getElementById('qrLabelModal')).show();
+            bootstrap.Modal.getOrCreateInstance(document.getElementById('qrLabelModal')).show();
         }
 
         // Make table rows clickable