fix: recompile duplicate-code-detector workflow (#7697)

## Summary

Clean recompile of the duplicate-code-detector workflow. The previous
commits by the coding agent incorrectly:

1. Hardcoded `sonnet-6x` model instead of using repository model
variables
2. Replaced SHA-pinned action refs (`github/gh-aw-actions/setup@<sha>`)
with unpinned tag refs
3. Removed the model multipliers merge step

The `.md` source was correct as-is — the original workflow failure was
caused by a missing `GH_TOKEN` (fixed separately), not a model
configuration issue.

## Changes

- Reverted `.md` source to main (no changes needed)
- Recompiled `.lock.yml` from clean source
- Only diff from main: default AI credits limit updated (`2000` →
`1000`) per compiler defaults

Author: lpcox