feat(split-meow): 搶救每筆支出幣別與匯率快照

[s123104]

摘要

搶救因 governance 分支被 PR #433 取代而遺失的 split-meow 每筆支出幣別+匯率快照功能（原 commit 87fcbe30，原屬已關閉路徑的 #411）。

背景

• 此功能修復 Codex 對 chore(ratewise): 生產治理 — PWA precache-first、ETag 修復、SEO 治理 #411 的 HistoryTab P2 評論：先 TWD 記帳後切 KRW，舊金額被誤格式化為 KRW
• 原在 chore/ratewise-production-governance（chore(ratewise): 生產治理 — PWA precache-first、ETag 修復、SEO 治理 #411）完成 + Playwright QA 驗收
• chore(ratewise): 生產治理 — PWA precache-first、ETag 修復、SEO 治理 #411 被 chore(ratewise): 生產治理 rebased on main（取代 #411） #433「rebased on main」取代，chore(ratewise): 生產治理 rebased on main（取代 #411） #433 僅保留 MoneyBox commit，此功能與 fix(ratewise): 為導覽 case-3 加上有界網路 fallback #426 002 稽核遺失 → 本 PR 搶救

變更

• ExpenseRecord 新增 currency + exchangeRateKrwPerTwd 快照欄位，記帳時保存
• HistoryTab 個別金額用各筆快照幣別、KRW 副標即時換算 TWD、彙總/結算採 trip 主導幣別 fallback
• 新增 formatKrwAsTwd helper；currencies.test 合併 main 完整版 + formatKrwAsTwd 測試
• 補 002：split-meow 幣別快照 + fix(ratewise): 為導覽 case-3 加上有界網路 fallback #426 SW bounded-nav 稽核條目

驗證

• ✅ split-meow vitest 175/175 通過
• ✅ typecheck 通過
• ✅ Playwright 瀏覽器驗收（原 chore(ratewise): 生產治理 — PWA precache-first、ETag 修復、SEO 治理 #411）：KRW 記帳 → 切回 TWD → 歷史仍顯示 ₩ + ≈ NT$ 換算

🤖 Generated with Claude Code

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Dependency Review

✅ No vulnerabilities or license issues or OpenSSF Scorecard issues found.

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