live_render: skip the per-frame PNG write once a window is showing

Image.fromarray(...).save() ran on EVERY frame regardless of whether a
window was already displaying it -- pure disk-I/O overhead adding to the
render-vs-game latency gap. Only write PNGs when there is no window (the
offline/headless case, where they are the actual output).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

emulator/firmware-decomp/emu860c/live_render.py

@@ -184,14 +184,17 @@ def feed_more(block):
 
 
 def present(img, nth):
-    Image.fromarray(img, 'RGB').save(os.path.join(HERE, 'live_%04d.png' % nth))
     if win is not None:
+        # live window: skip the per-frame PNG write (a real disk-I/O cost
+        # that was adding latency for no benefit once a window is showing)
         import pygame
         surf = pygame.surfarray.make_surface(np.transpose(img, (1, 0, 2)))
         win.blit(surf, (0, 0)); pygame.display.flip()
         for ev in pygame.event.get():
             if ev.type == pygame.QUIT:
                 return False
+    else:
+        Image.fromarray(img, 'RGB').save(os.path.join(HERE, 'live_%04d.png' % nth))
     return True