Revert regex pattern to string interpolation - concatenation broke GUID extraction

The concatenation approach suggested by Copilot broke the regex matching.
Reverting to the original string interpolation which works correctly.

String interpolation in static contexts is fine for this use case.

Author: liamgold

src/Services/ContentHubLinkService.cs

@@ -38,7 +38,7 @@ public class ContentHubLinkService : IContentHubLinkService
     // Matches /getcontentasset/{contentItemGuid}/{assetGuid}
     // Guid.TryParse() handles actual GUID validation, so we just capture word characters and hyphens
     private static readonly Regex contentItemLinkRegex = new(
-        @"\/getcontentasset\/(?<" + CONTENT_ITEM_GROUP_NAME + @">[\w-]+)\/[\w-]+",
+        $@"\/getcontentasset\/(?<{CONTENT_ITEM_GROUP_NAME}>[\w-]+)\/[\w-]+",
         RegexOptions.Compiled | RegexOptions.IgnoreCase
     );