Pin Duplicate Code Detector to priced Copilot model to avoid unknown-model AI credit failures (#4942)

* Initial plan

* fix: pin duplicate-code-detector to priced copilot model

* Recompile lockfile to include agent_model in metadata

The compiler now correctly emits agent_model:gpt-5.4-mini in the
metadata header, consistent with other pinned-model workflows.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

---------

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: Landon Cox <landon.cox@microsoft.com>
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: 3 people

.github/workflows/duplicate-code-detector.lock.yml

@@ -25,6 +25,10 @@ tools:
     toolsets: [issues]
   bash: true
 
+engine:
+  id: copilot
+  model: gpt-5.4-mini
+
 safe-outputs:
   threat-detection:
     enabled: false