docs: add speed vs accuracy scatter plot to benchmark and README

WER vs RTF scatter plot showing all backend/policy/model combos
on the 30s English file. Sweet spot zone highlights the best
tradeoffs. Added to both BENCHMARK.md and README.md.

BENCHMARK.md

@@ -66,6 +66,10 @@ Ground truth transcripts (`.transcript.json`) with per-word timestamps are hand-
 <img src="benchmark_chart.png" alt="Benchmark comparison on 30s English" width="800">
 </p>
 
+<p align="center">
+<img src="benchmark_scatter.png" alt="Speed vs Accuracy tradeoff" width="700">
+</p>
+
 ### French (16.3 s, 1 speaker, `--language fr`)
 
 | Backend | Policy | Model | RTF | WER | Timestamp MAE |

README.md

@@ -82,7 +82,12 @@ Go to `chrome-extension` for instructions.
 | *[Not recommanded]*  Speaker diarization with Diart | `diart` |
 
 See **Parameters & Configuration** below on how to use them.
-See **[BENCHMARK.md](BENCHMARK.md)** for detailed performance comparisons across all backends.
+
+<p align="center">
+<img src="benchmark_scatter.png" alt="Speed vs Accuracy tradeoff" width="700">
+</p>
+
+See **[BENCHMARK.md](BENCHMARK.md)** for the full benchmark with tables, model size comparison, and more.