docs: refresh BU Bench harness plot with current model results

Propagates browser-use/benchmark-x-laminar@45b563b. The README copies were
generated 2026-07-29 and predate seven changes to the plot:

  - claude-opus-5 (87.0%), claude-fable-5 (87.0%), grok-4.5 (86.3%),
    kimi-k3 (86.0%), gpt-5.6-sol/terra/luna, qwen3.8-max (79.0%) and
    deepseek-v4-flash-0731 (76.0%) added
  - base deepseek-v4-flash and gpt-5.6-luna-medium dropped
  - open-weight bars are now a gray fill with a blue dashed outline
    instead of a solid blue fill

Author: Alezander9