[LivXue]

Summary

Update the hosted AI4AI (Nanochat 50M Pretraining) chart reference in both bilingual READMEs.

• Replace the old image attachment URL in README.md and README.zh-CN.md.
• Use the updated chart with the Bits Per Byte (BPB) label and the Lower Is Better annotation above the BPB values.
• Keep the chart hosted as a GitHub attachment; no image binary is added to the repository.

Type

• Fix
• Feature
• Docs
• CI / tooling
• Refactor
• Other

Verification

• Relevant tests pass locally
• Relevant lint / type checks pass locally
• User-facing docs or screenshots are updated when needed

Commands:

• git diff --check
• UV_NO_SYNC=1 make check-large-files check-source-language PYTHON_VERSION=.venv/bin/python COMMIT_RANGE=HEAD
• UV_NO_SYNC=1 uv run --no-sync pytest tests/test_readme_scope_canon.py tests/test_cli_onboard_commands.py -k readme_quickstart -q
• Downloaded attachment SHA-256 matches the local PNG.

Risk

• Security impact considered
• Backward compatibility considered
• Rollback path is clear for risky changes

This is a documentation-only URL update. Reverting the commit restores the previous chart.

Related Issues

#465

[ZuyiZhou]

Approving. Two lines, one asset id, the same swap in both files.

I fetched both PNGs and compared them: every number is identical -- BPB 1.053 / 1.038 / 1.037, runtime 4.99 / 4.90 / 3.74, tokens 13.35 / 9.38 / 3.79, cost $50.00 / $39.40 / $0.97, the same three series and the same 2x A800 note. So this is a cosmetic refresh, not a new measurement, and nothing in the surrounding prose needed to move with it. The BPB panel now carries its unit in the heading (Bits Per Byte (BPB)) instead of on a line below, which is what the alt text already said, and it gains a "lower is better" arrow.

One nit, not worth a round trip: "Lower Is Better" now appears twice, top right for the figure and again inside the BPB panel. It is true of all four panels, so the per-panel one reads as if it were not.

The red check is not this PR. unit (py3.12 / 1/4) reports 5489 passed, 9 skipped; what failed the job is --idle-ceiling-strict tripping on tests/test_ppt_engine_assets_script_helpers.py::test_a_formula_that_stacks_is_typeset_as_a_picture_in_the_decks_ink at 5.76s idle -- a runner-speed flake in the deck engine that a two-line README edit cannot reach. main's last two runs are green. Worth a re-run before merging rather than a change here.