docs(ui): stop claiming a .bar-label alias the stylesheet no longer has

[argszero]

Summary

The comment above .bar-row .bar-top in ui/css/style.css claimed that the
live stylesheet also answers to .bar-label:

/* .bar-row .bar-top：原型「名称左 / 数值右」的行头（线上 .bar-label 为其别名） */

That is false. git grep -n 'bar-label' over the whole tree returns exactly
one hit — that comment. There is no .bar-label rule, no markup emits the
class, and the design baseline docs/prototype/aitokenpool-console.html does
not carry it either. All three possible consumers (stylesheet rule /
implementation / prototype) are absent, so writing class="bar-label" today
matches nothing at all.

The alias claim is not stale drift in the usual sense: git show 75dcb2c
(#154, the shared component layer) is the commit that removed the name —
it deletes .bar-row .bar-label and adds .bar-row .bar-top, and its message
reads bar-label/bar -> bar-top/bar-track/bar-fill. The sentence asserting an
alias was written by the same commit that dropped the thing it points at.

#154 left two such breadcrumbs. #316 fixed the .stat one
(.stat-card); this is the second. The wording here mirrors the phrasing
#316 landed — name the historical name and say there is no alias rule, instead
of inventing one. (Adding a real .bar-label rule was the rejected alternative
in both cases: the code emits .bar-top, and nothing else consumes
.bar-label.)

Related Issue

None.

Changes

• ui/css/style.css: the .bar-row .bar-top comment now names
  .bar-label as the historical name feat(ui): add shared component layer (stat-card/pill/tag/toolbar/bar-list) + define missing button variants (rant 2026-09-11, PR3) #154 replaced and states there is no
  alias rule.
• ui/index.html: css/style.css?v=20260924-2 → ?v=20260924-3
  (this file's history bumps the token with every style.css change).
• 涉及配置/数据结构的改动已同步示例文件 — not applicable.

Tests

• cargo test — 413 passed; 0 failed
• cargo fmt --check — clean
• cargo clippy --all-targets -- -D warnings — clean
• 新增/更新了单元测试（如适用） — not applicable: comment-only change,
  no behaviour to assert.

Checklist

• 分支命名符合约定 (docs/)
• Commit message 使用 Conventional Commits 格式
• 单一职责，改动最小化

[argszero]

Self-review (committer; allow_self_merge is enabled for this task).

Claim checked against the tree at 1da8a39:

• git grep -n 'bar-label' → exactly one hit, the comment being changed. No
  rule, no markup, no prototype occurrence.
• git show 75dcb2c -- ui/css/style.css → -.bar-row .bar-label,
  +.bar-row .bar-top; commit message: bar-label/bar -> bar-top/bar-track/bar-fill.
  The alias claim was authored by the commit that deleted the alias.
• app.js:2987 (barRow()) emits class="bar-row" + class="bar-top" — the
  documented producer agrees with the surviving rule, not with the removed name.

Related commit / scope: same commit as #316 (.stat → .stat-card); that
one fixed the first false breadcrumb, this fixes the second. Wording mirrors
what #316 landed, so the two now read consistently.

Verified: cargo test 413/0, cargo fmt --check clean,
cargo clippy --all-targets -- -D warnings clean; both CI jobs green.
Diff is one comment plus the style.css?v= token.

Merging.