docs: add best models plot

[Alezander9]

Summary

• Add the BrowserCode best-models light/dark plot assets to the README.
• Place the new plot above the all-model performance chart.
• Update recommended model bullets to match the current BU Bench categories.

Testing

• bun turbo typecheck --filter='@browser-use/browsercode-core...' --filter='@browser-use/bcode-browser' --filter='@browser-use/bcode-laminar' (pre-push hook, cached)

---

Summary by cubic

Add light/dark “best models” plot to the README and place it above the all-model performance chart. Update the recommended model list to match current BU Bench categories for quicker model selection.

^{Written for commit 98380cd. Summary will update on new commits.}

[cubic-dev-ai]

No issues found across 3 files

_{Re-trigger cubic}