docs: update all-model performance plots

[Alezander9]

Summary

• Replace the BrowserCode all-model performance chart light/dark PNGs with the latest benchmark-generated versions.
• Keep the existing README image paths and formatting unchanged.

Testing

• Verified copied PNG hashes match benchmark-x-laminar outputs.
• bun turbo typecheck --filter='@browser-use/browsercode-core...' --filter='@browser-use/bcode-browser' --filter='@browser-use/bcode-laminar' (pre-push hook, cached)

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Summary by cubic

Update BrowserCode all-model performance plots to the latest benchmark-generated images. Replaced the light and dark PNGs; README image paths remain unchanged.

^{Written for commit 6cde600. Summary will update on new commits.}

[cubic-dev-ai]

No issues found across 2 files

_{Re-trigger cubic}