docs(ui): state the inlineForm validate contract the code implements

[argszero]

Summary

ui/README.md:90 (the ## 行内组件约定 section, "禁用原生弹窗" bullet) said an inlineForm opts.validate error is surfaced as "toast + 重新聚焦". The code has not done that since 2d492ee (#47): ui/js/app.js's finish() calls setFieldError(input, err) — no toast, no explicit refocus.

The same file already states the correct behaviour, at line 133 (## 一致性约定, "行内编辑校验"): "inlineForm 的 opts.validate 失败走 setFieldError（红边框+行内文案）… 不使用 toast 承载错误". So the document contradicted itself, and only line 90 was wrong.

Provenance is drift, not a trade-off:

• 990cd5a (feat(ui): replace native confirm/prompt dialogs with inline components (v1.17 A) #41, v1.17 A) — inlineForm was born with if (err) { toast(err, "error"); input.focus(); return; }, so line 90 was true when written.
• 2d492ee (feat(ui): detail consistency — inline errors in editors, unified phrasing (v1.17 G) #47, v1.17 G) — the same commit changed that line to setFieldError(input, err) and added the ## 一致性约定 section (line 133) stating the new rule, but did not update line 90.

grep -rn "重新聚焦" over the repository matched this one line only, and no gate in src/ quotes it — it is prose nothing pins, which is exactly how it survived.

Related Issue

None. Found during reconnaissance; no issue was opened for it.

Changes

• ui/README.md — line 90's parenthetical now reads `opts.validate` 失败走 `setFieldError`（红边框+行内文案），不使用 toast, matching line 133 and ui/js/app.js. One line; docs only. No cache-bust token: ui/README.md is not a served asset.

• 功能/修复说明 (prose only: one stale contract corrected to the implemented behaviour)

• 涉及配置/数据结构的改动已同步示例文件 (not applicable — no config/data change)

Tests

• cargo test 全部通过 — 426 passed; 0 failed
• cargo fmt --check 通过
• 新增/更新了单元测试（如适用）— not applicable. Docs-only, and this repository's settled convention for prose claims (doc-comment-claims axis, 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/fix(admin): state the refusal a deleted model now meets, not the old zero bill #312–fix(i18n): drop the retired "shown once" claim from the generate-key toast #320) is to correct the data rather than gate it; the phrase is not an invariant a lexical gate can hold without an exemption list.

Checklist

• 分支命名符合约定（docs/）
• Commit message 使用 Conventional Commits 格式（docs(ui): ...）
• 单一职责，改动最小化 (1 file, +1/−1)

[argszero]

Self-review (Committer, allow_self_merge): CI green — msrv pass, test / fmt / clippy pass (426 tests, 0 failed). Diff is a single docs line; local cargo test / cargo fmt --check / cargo clippy --all-targets -D warnings all pass (note ui/README.md is include_str!-ed at src/state_gate.rs:12457, so the full suite was re-run for this docs change). No review feedback outstanding. Merging.