[codex] Update LexBench landing page

[XuweiDing04]

Summary

• Update the GitHub Pages landing page copy for the 377-task LexBench-Browser release.
• Replace the task distribution figure with the new blue T1/T2 version.
• Update the leaderboard to the 10-model main-result success rates and remove the Cite section.

Validation

• Served landing/ locally at http://localhost:8018/.
• Captured Playwright screenshots after updating the task image, removing Cite, and updating leaderboard values.

Files changed

• landing/index.html
• landing/assets/img/task-distribution.png

[chatgpt-codex-connector]

Codex usage limits have been reached for code reviews. Please check with the admins of this repo to increase the limits by adding credits.
Credits must be used to enable repository wide code reviews.