fix(ui): restore the digit shortcut for the settings view

[argszero]

Summary

The sidebar advertises a digit shortcut on every nav item, but the global keydown guard hard-coded the range 1-7. NAV_ORDER now has 8 items (ops was inserted before settings), so settings renders the badge "8" and its tooltip says to press it — while pressing 8 is silently ignored. The view was unreachable by digit key while advertising that it was reachable.

ui/README.md documented 1-7 correctly: it was a faithful description of a buggy guard, not a doc drift. Provenance: ad631ae (#44) wrote the range when NAV had exactly 7 items; 85982e8 (#80) inserted ops before settings and the range was never widened.

Related Issue

Changes

• ui/js/app.js: the digit guard no longer writes a bound at all — the badge is NAV_ORDER index + 1 and the handler resolves the item from the same array, so an out-of-range digit is a no-op and badge/key range can never diverge again. (Simply bumping "7" → "8" would re-arm the identical bug at the next view insertion; the controls below demonstrate exactly that.)
• ui/js/app.js: help-panel key row 1–7 → 1–8; the two comments that asserted 1-7 now state the count-independent rule (1..N, N = NAV_ORDER.length).
• ui/css/style.css: comment 数字 1-7 切换视图 → 数字键切换视图.
• ui/README.md: 1-7 → 1-8 (view list corrected to all 8 in NAV_ORDER order); help row 1–7 → 1–8; kbd-guard line de-numbered. Plus 4 more stale current-state counts from the same sweep, each against an arbiter that is itself asserted:
  • language-pack keys 733 → 785 (src/i18n_pack.rs ZH_KEY_COUNT/EN_KEY_COUNT, enforced by cargo test)
  • referenced-key scan 496 → 680 (T() literals 430 + data-i18n* 305, deduplicated)
  • toast() call sites 39 → 75
  • document.title coverage 7 个视图 → 8 (VIEW_TITLE has 8 keys)
• ui/index.html: cache-bust 20260912-3 → 20260912-4 (5 refs).
• 涉及配置/数据结构的改动已同步示例文件 — N/A: no config or schema change.

No i18n key change: help.k2's value is range-free in both packs (切换侧边栏视图 / Switch sidebar view), so no pack edit and no gate-constant change was needed.

Tests

• cargo test 全部通过 — 165 passed / 0 failed
• cargo fmt --check 通过
• cargo clippy --all-targets -- -D warnings 通过
• node --check ui/js/app.js 通过
• 新增/更新了单元测试（如适用） — not applicable: the change is in ui/ JS, which has no test harness in this repo; the i18n/key gates (src/i18n_pack.rs) still pass unchanged. Verification was done with an A/B probe over the real sources instead:
  • guard range read out of the source and evaluated against synthetic key events (the probe does not look for the literal 7/8, so it stays valid after the guard is rewritten)
  • before (HEAD): RESULT: FAIL (1 advertised shortcut(s) do nothing), exit 1 → after: RESULT: OK (every advertised shortcut works), exit 0
  • controls: hard-coding "7" on the fixed tree reproduces the failure; hard-coding "8" also fails once a 9th view is added, while the derived guard passes in the same 9-view tree — i.e. the fix removes the class, not the instance

Checklist

• 分支命名符合约定 (fix/)
• Commit message 使用 Conventional Commits 格式 (fix(ui): …)
• 单一职责，改动最小化 — one defect (the digit shortcut) + the same-file claim refresh found by the same sweep; no opportunistic refactor