docs: FinanceBench chart as local light/dark assets (#440)

* docs: swap the FinanceBench chart for local light/dark assets

Claude-Session: https://claude.ai/code/session_012edjBdTjAM24UAZGyq6TfF

* docs: replace the FinanceBench chart with light/dark assets

Claude-Session: https://claude.ai/code/session_012edjBdTjAM24UAZGyq6TfF

* docs: narrow the FinanceBench chart to 60%

Claude-Session: https://claude.ai/code/session_012edjBdTjAM24UAZGyq6TfF

* docs: set the FinanceBench chart to 65%

Claude-Session: https://claude.ai/code/session_012edjBdTjAM24UAZGyq6TfF

* docs: set the FinanceBench chart to 70%

Claude-Session: https://claude.ai/code/session_012edjBdTjAM24UAZGyq6TfF

README.md

@@ -444,13 +444,14 @@ Full results, data, and the runner are in the [benchmark repo](https://github.co
 
 PageIndex reached a state-of-the-art [**98.7% accuracy**](https://vectify.ai/blog/Mafin2.5) on [FinanceBench](https://arxiv.org/abs/2311.11944) (financial document QA benchmark), vastly outperforming vector-based RAG.
 
-<!--
 <div align="center">
-  <a href="https://github.com/VectifyAI/Mafin2.5-FinanceBench">
-    <img src="https://github.com/user-attachments/assets/571aa074-d803-43c7-80c4-a04254b782a3" width="70%">
-  </a>
+<a href="https://github.com/VectifyAI/Mafin2.5-FinanceBench">
+<picture>
+  <source media="(prefers-color-scheme: dark)" srcset="assets/financebench-dark.png">
+  <img src="assets/financebench-light.png" width="70%" alt="FinanceBench accuracy: PageIndex 98.7%, vector RAG 50%.">
+</picture>
+</a>
 </div>
--->
 
 Explore the full FinanceBench [evaluation results](https://github.com/VectifyAI/Mafin2.5-FinanceBench) and the [blog post](https://vectify.ai/blog/Mafin2.5).