feat(ui): marketplace row expand — max tokens, price conversion, multi-key failover detail (v1.19 F)

[argszero]

Summary

UI/UE 4th-round deepening — item F: marketplace row expand details (rant 2026-08-17T20:39:30, v1.19).

Each marketplace row gets a +/− expand toggle (.row-expand in the first column). Clicking appends a detail row (.mk-detail, colspan=7, inline — no modal) showing:

• Max tokens (single-call output cap from D.MODELS; "未公布" when unlisted)
• Price conversion — 1M tokens ≈ N 点 (at output price) + input price /1M
• Context length (D.ctxFmt)
• Availability (可用/繁忙 + success rate)
• Multi-key auto-failover note — shown only for multi models (architecture v0.2 routing policy)

Behavior:

• Only one row expanded at a time — clicking another row switches; clicking the same row collapses
• Expanded state lives in mkExpanded (data, not DOM) — survives search/filter re-renders
• Event handled in the existing #mk-body click delegation ([data-mk-expand] branch, before [data-use-model])
• Mobile card mode: detail td has no data-label (empty ::before), so the card shows just the detail grid; auto-fit columns adapt

Docs: docs/user-stories.md v1.19 (item F) + ui/README.md「市场行展开约定」. Verified by DOM-stub smoke test (21 assertions: initial state, expand/collapse, max tokens, price conversion, failover note, single-expand switching, max-unlisted fallback, data-state persistence across search re-render, CSS structure), cargo test, cargo fmt --check.

Rant (verbatim)

Rant: UI/UE 第四轮多角度深化 — 状态保持、信息密度、原生控件美化、帮助可达性（宿主 2026-08-17 第四轮指示：继续从多角度美化 UI、优化 UE）

F. 市场模型行展开详情

• 市场表格每行加展开按钮（+/-）：展开显示 max tokens、价格换算说明（1M tokens ≈ N 点）、可用性详情（多 key 故障转移说明）
• 行内展开（tr 下追加一行），不弹窗；仅展开当前行，点其它行自动收起

Related

• Rant timestamp: 2026-08-17T20:39:30.507364 (project aitokenpool, status in_progress; A = feat(ui): URL hash routing — share/bookmark/refresh restore (v1.19 A) #55, B = feat(ui): transactions summary bar — income/expense/net tied to tab & column filters (v1.19 B) #56, C = feat(ui): custom SVG select arrow — appearance:none, themed, hover/focus like input (v1.19 C) #57, D = feat(ui): toast queue — stack up to 3, independent fade in/out, keep grading styles (v1.19 D) #58, E = feat(ui): shortcuts help panel — ?/Shift+/ toggle, Esc close, view+theme context (v1.19 E) #59 merged)
• Branch: feat/ui-ue-round4-market-expand (per rant: 分支 feat/ui-ue-round4; item G to follow)

Tests

• DOM-stub smoke test — 21/21 assertions pass
• node --check ui/js/app.js
• cargo test — 1 passed
• cargo fmt --check