feat(ui): table density toggle — comfortable/compact radio, localStorage, site-wide .density-compact (v1.20 C)

[argszero]

Summary

Item C of rant 2026-08-17T20:46:57 (UI/UE 第五轮多角度深化, v1.20): 表格密度切换 — table density toggle in Settings.

• Settings → 偏好 (Preferences) card gains a 「表格密度」 two-option radio group (input[name="density"]):
  • #density-comfortable — 舒适（默认）/ comfortable (default, checked)
  • #density-compact — 紧凑 / compact
  • Vertical .density-options layout with accent radio dots, consistent with the existing label.check pattern
• localStorage atp-density memory: restored on load (radio pre-selected), updated on every change; try/catch guards privacy mode
• Switching applies/removes a .density-compact modifier class on #app, which tightens all .table site-wide via CSS:
  • th/td padding 10px 8px → 4px 8px, td font-size 12px, th/inline buttons 11px
  • Comfortable mode untouched (zero regression, no rules emitted)
• Works with every existing .table (API keys, transactions, marketplace, sharing, admin) without per-table changes

Rant reference (verbatim)

C. 表格密度切换 — 设置页「偏好」区两档单选（舒适/紧凑），localStorage 记忆，.table density 修饰类（紧凑 → 行 padding 减小、字号 13px），所有表格统一生效

Verification

• DOM-stub smoke test: 13/13 assertions pass (default comfortable, toggle→class+storage, restore on reload, HTML/CSS structure)
• node --check ui/js/app.js ✓, CSS braces balanced (331/331)
• cargo test ✓ (1 passed), cargo fmt --check ✓
• Docs: docs/user-stories.md v1.20 entry updated (A feat(ui): first-login onboarding tour — 4-step spotlight highlight, skip/prev/next/finish, replay from settings (v1.20 A) #63 / B feat(ui): interactive copy-toast with endpoint CTA — jump to settings, flash endpoint card (v1.20 B) #65 marked merged, C added), ui/README.md「表格密度切换约定」section added

Progress on rant 20:46:57: A (#63) + B (#65) + C (#66) merged; remaining D–G.