docs(ui): drop the pasted duplicate sentence from the data notes

[argszero]

Summary

ui/README.md §数据说明 states the chat-mock billing rule twice, verbatim: once as its own bullet (- 消费模拟（聊天 Mock）按 输出参考价 × 0.19M tokens 计费…), and once pasted onto the tail of the multi bullet, where it is joined to an unrelated fact by a semicolon. This PR removes the pasted copy; the dedicated bullet keeps the rule.

Related Issue

None (self-found during a documentation audit; no tracking issue exists).

Changes

• Delete the pasted duplicate sentence from the end of the 市场模型带 multi 标记… bullet in ui/README.md; that bullet now ends at …已随文档精简合并到此节） where it belongs.
• The dedicated bullet for the billing rule is left untouched — it is where the sentence belongs.
• No configuration/data-structure changes, so no example-file sync is required.

Origin of the duplication. 9a3ff3e (#22) first wrote the sentence at the tail of the multi bullet. 500e17d (#27) added the dedicated bullet but did not remove the original, so the sentence has appeared twice since 2026-08-17. A sweep of every tracked *.md (clauses of ≥25 chars occurring more than once) finds this as the only duplicated long clause in the repository, and it now returns zero.

Tests

• cargo test — 426 passed; 0 failed
• cargo fmt --check — clean (rc 0)
• cargo clippy --all-targets -- -D warnings — clean (rc 0)
• New/updated unit tests — not applicable: ui/README.md is prose, and the repo's settled convention for this class (doc-comment-claims axis) is to fix the value, not to add a gate. Precedents: docs(perf_gate): drop the stale file count from the gate header #309/docs(ui): stop restating the i18n counters and correct two stale gate claims #310/docs(ui): describe the recent-models store the code actually keeps #313/docs(ui): describe the login page the two-column redesign left behind #314/docs(ui): name only the bump sites, test and hint the code still has #315/docs(ui): stop claiming a .bar-label alias the stylesheet no longer has #317/docs(ui): name the operator card the way the code names it #319/fix(i18n): drop the retired "shown once" claim from the generate-key toast #320/docs(ui): name the translator helper the code actually declares #322/docs(ui): state the inlineForm validate contract the code implements #324/docs(ui): complete four stale capability lists in ui/README.md #325.

Checklist

• Branch name follows the convention (docs/<description>)
• Commit message uses Conventional Commits (docs(ui): …)
• Single responsibility, minimal change (1 file, +1/−1)

[argszero]

Self-review (committer, allow_self_merge: true).

Verified against the tree this branch is based on (9df6d00):

1. The sentence 消费模拟（聊天 Mock）按 输出参考价 × 0.19M tokens 计费…（US-6） appeared verbatim twice in ui/README.md — as its own bullet and pasted onto the tail of the multi bullet. After this change it appears once, on its own bullet.
2. A sweep of every tracked *.md (clauses of ≥25 chars occurring more than once) returned this as the only duplicated long clause before the change, and returns nothing after it.
3. The removed text is byte-identical to the retained bullet, so no information is lost. The rule itself is still accurate (ui/js/app.js sets the mock to 0.19 tokens), and US-6 remains a live tag used across ui/js/app.js, ui/index.html, ui/css/style.css — so neither the number nor the tag was ever the problem; only the duplication was.

ui/README.md is include_str! corpus, so the full suite was re-run: cargo test 426/0, cargo fmt --check rc 0, cargo clippy --all-targets -- -D warnings rc 0.

Documentation-only change; no gate added, consistent with the repo's doc-comment-claims convention.