fix(python): avoid backslashes inside f-string expressions in debug_compile HTML

app.py

@@ -519,7 +519,9 @@ This is a debug build generated at \today.
         _write_logs(LOG_PATH, logs)
         return (
             "<div style='color:#b00'><b>Debug PDF compile failed.</b></div>"
-            + f"<pre style='white-space:pre-wrap;background:#f7f7f8;padding:8px;border-radius:6px'>{'\n'.join(logs)}</pre>"
+            + "<pre style='white-space:pre-wrap;background:#f7f7f8;padding:8px;border-radius:6px'>"
+            + "\n".join(logs)
+            + "</pre>"
         )
 
     # Build preview + open-new-tab link
@@ -529,7 +531,9 @@ This is a debug build generated at \today.
         html = (
             f"<div style='margin-bottom:8px'>{open_tab}</div>"
             + _pdf_to_iframe_html(pdf_path, height="700px")
-            + f"<pre style='white-space:pre-wrap;background:#f7f7f8;padding:8px;border-radius:6px;margin-top:8px'>{'\n'.join(logs[-60:])}</pre>"
+            + "<pre style='white-space:pre-wrap;background:#f7f7f8;padding:8px;border-radius:6px;margin-top:8px'>"
+            + "\n".join(logs[-60:])
+            + "</pre>"
         )
         _write_logs(LOG_PATH, logs)
         return html