feat(ui): interactive copy-toast with endpoint CTA — jump to settings, flash endpoint card (v1.20 B)

[argszero]

Summary

UI/UE 5th-round deepening — item B: copy-key next-step guidance (rant 2026-08-17T20:46:57, v1.20).

After copying an API Key successfully, the toast becomes interactive — text + an embedded 「配置接入端点 →」 button:

• toast(msg, type, opts) extended with opts.action = { label, onClick }:
  • Renders an inline .toast-action button (accent pill, hover inverse)
  • Extends display time from 2.6s to 6s (TOAST_ACTION_MS) so users have time to click
  • No-action toasts keep the textContent path — zero regression (39 existing call sites untouched)
• copyKey success path (both clipboard API and execCommand fallback) shows the CTA
• Clicking it calls gotoEndpointCard(): switchView("settings") (idempotent — already on settings just stays) → #endpoint-card gets .ep-flash (accent ring pulse 0.8s ×2, replayed via remove→reflow→add) → scrollIntoView({behavior:"smooth", block:"center"})
• Forms the complete "copy key → configure endpoint" loop with the 20:44:18 endpoints card

Docs: docs/user-stories.md v1.20 + ui/README.md「可交互 toast / 复制后引导约定」. Verified by DOM-stub smoke test (15 assertions: CTA button on copy success, success grading kept, onClick bound → view switch + flash + scroll, idempotent re-copy on settings, longer display-time constant, plain toast regression, CSS), cargo test, cargo fmt --check.

Rant (verbatim)

Rant: UI/UE 第五轮多角度深化 — 首次引导、复制后续引导、密度切换、最近使用、CSV 导出、表格键盘导航、品牌氛围（宿主 2026-08-17 第五轮指示：继续从多角度美化 UI、优化 UE）

B. 复制 Key 后的下一步引导

• 复制 API Key 成功后，toast 变为可交互：文案 + 「配置接入端点 →」按钮；点击切到设置页并滚动到接入端点卡片、高亮闪烁
• 已在设置页时直接高亮端点卡片；简单实现：toast 内嵌按钮，点击调 switchView('settings') + 卡片闪一下

Related

• Rant timestamp: 2026-08-17T20:46:57.465428 (project aitokenpool, status in_progress; A = feat(ui): first-login onboarding tour — 4-step spotlight highlight, skip/prev/next/finish, replay from settings (v1.20 A) #63 merged)
• Branch: feat/ui-ue-round5-copy-next (per rant: 分支 feat/ui-ue-round5; items C–G to follow)

Tests

• DOM-stub smoke test — 15/15 assertions pass
• node --check ui/js/app.js
• cargo test — 1 passed
• cargo fmt --check