Log gpu_duration and mode at infer start

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

app.py

@@ -359,7 +359,7 @@ def _infer_gpu(pil_images, prompt, seed, guidance_scale, steps, width, height, m
     t0 = time.perf_counter()
 
     print(f"[infer] ===== START =====")
-    print(f"[infer] steps={steps}, guidance={guidance_scale}, seed={seed}")
+    print(f"[infer] steps={steps}, guidance={guidance_scale}, seed={seed}, gpu_duration={gpu_duration}s, mode={mode}")
     print(f"[infer] prompt={repr(prompt[:120])}")
 
     if _cuda_ok: