fix(ci): install opencv-python-headless for the TableFormer export step

docling_ibm_models's tf_predictor imports cv2, but publish-models.yml only
installed docling_ibm_models/onnxscript/onnxruntime/huggingface_hub, so the
export step failed with ModuleNotFoundError: No module named 'cv2'.
scripts/pdf_setup.sh never hit this because it installs the full `docling`
package instead, which pulls opencv in transitively.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01DofkqhMuAJbL9arnnuVisL

Author: claude

.github/workflows/publish-models.yml

@@ -57,7 +57,7 @@ jobs:
       - name: Install TableFormer export deps
         continue-on-error: true
         id: tf-deps
-        run: pip install docling_ibm_models onnxscript onnxruntime huggingface_hub
+        run: pip install docling_ibm_models onnxscript onnxruntime huggingface_hub opencv-python-headless
 
       - name: Export TableFormer
         if: steps.tf-deps.outcome == 'success'