Add image preview box; serve PDF preview via iframe /file=; hook image render after run; fix merge markers

app.py

@@ -1465,6 +1465,7 @@ This work, developed in collaboration with [TVG@Oxford](https://torrvision.com/i
         inputs=[arxiv_in, pdf_in, key_in, inst_logo_in, conf_logo_in, theme_in],
         outputs=[logs_out, pdf_out, pdf_file_out, zip_out, overleaf_out],
     )
+    _run_evt.then(fn=preview_image_from_pdf, inputs=[pdf_file_out], outputs=[img_out])
     debug_zip_btn.click(fn=debug_compile_output_zip, inputs=[], outputs=[debug_zip_out])
     debug_last_btn.click(fn=debug_compile_last_pipeline_zip, inputs=[], outputs=[debug_last_out])