fix(fingerprint): propagate htmlHash through trimElementSpec serialization

htmlHash was computed on DqElement and included in toJSON, but
trimElementSpec in process-aggregate.js builds the final node output
from scratch and was not copying it through.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: Abhishek Bindra

lib/core/reporters/helpers/process-aggregate.js

@@ -103,5 +103,9 @@ function trimElementSpec(elmSpec = {}, runOptions) {
   if (runOptions.xpath) {
     serialElm.xpath = elmSpec.xpath ?? ['/'];
   }
+  // [a11y-core]: propagate htmlHash to final output
+  if (elmSpec.htmlHash) {
+    serialElm.htmlHash = elmSpec.htmlHash;
+  }
   return serialElm;
 }