Add heatmap weighted cost: 47% less face error at budget=64

- cuda/make_heatmap.py: OpenCV Haar face+edge detection → uint8 weight map
- cuda/prng_budget_search.cu: --weight-map arg, weighted kernel delta
- data/che_weighted64_anim.json: 25-frame weighted animation (2585 seeds)
- data/che_unweighted64_anim.json: 25-frame unweighted for comparison
- docs/renderer.html: two new presets (weighted👁 / unweighted-64)
- media/prng_images/heatmap_comparison.png: visual comparison gallery

Result: face zone error 21.9%→11.5% (−47%) at budget=64 seeds/frame,
cost: +5.7% overall. Sweet spot for low-bitrate streaming animation.

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

Author: oisee

data/che_unweighted64_anim.json

@@ -359,6 +359,10 @@ <h3>seeds <span style="color:#3a3a3a;font-size:9px">click = toggle one</span></h
    paths:['../data/foveal_cascade_seeds.json','data/foveal_cascade_seeds.json']},
   {id:'che_anim',label:'Che animation 🎬',  meta:'25 frames · 16,114 seeds · 0.07% avg · delta',
    paths:['../data/che_anim_flat.json','data/che_anim_flat.json']},
+  {id:'che_wgt64',label:'Che weighted 👁 (64)',  meta:'25 frames · 2585 seeds · heatmap face · 47% less face err',
+   paths:['../data/che_weighted64_anim.json','data/che_weighted64_anim.json']},
+  {id:'che_unw64',label:'Che unweighted (64)',  meta:'25 frames · 2585 seeds · no heatmap · compare',
+   paths:['../data/che_unweighted64_anim.json','data/che_unweighted64_anim.json']},
   {id:'bgt_a',label:'Budget A · KF256/DT128', meta:'10 frames · 1384 seeds · shrink=0.90 · 23%→14%',
    paths:['../data/budget_conf_a.json','data/budget_conf_a.json']},
   {id:'bgt_b',label:'Budget B · KF128/DT64',  meta:'10 frames · 704 seeds · shrink=0.70 · vignette',