Lower @spaces.GPU duration from 300s to 60s

The duration arg is a per-call quota guard, not a charge — actual time
used is what gets billed. Setting it at 300s was right at ZeroGPU's
free-user single-call limit, which blocked free users from the space.

Typical Qwen edit lands ~13s wall-clock from the client side (less
inside the GPU function once you strip queue + network), so 60s leaves
~5x safety buffer for slower edits while unblocking free users.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

app.py

@@ -138,7 +138,7 @@ def use_output_as_input(output_images):
     return output_images
 
 # --- Main Inference Function (with hardcoded negative prompt) ---
-@spaces.GPU(duration=300)
+@spaces.GPU(duration=60)
 def infer(
     images,
     prompt,