fix(split-meow): 混幣行程顯示警告並停止跨幣別錯誤加總

[s123104]

背景

Codex 三方 review(Q3)發現 split-meow 的 production bug(已隨 #445 上線):當同一行程記到多種幣別(使用者在 Settings 中途切換全域幣別)時,totalSpent/balances/settlements 直接把不同幣別的數字相加,並以單一幣別標籤顯示——產生看似精準實則錯誤的總額與結算,Codex 評為「比沒有總額更糟」。

註:tripCurrency = tripExpenses[length-1] 取的是最舊一筆(store prepend),這與註解「trip 建立時的幣別」意圖一致,非 bug;真正問題是跨幣別加總。

修法(最小生產級安全修復)

• 偵測 isMixedCurrency(trip 內出現 >1 種幣別)。
• 混幣時:隱藏單一總額與結算區塊,改顯示警告(四語系 zh-TW/en/ko/ja),引導改用單一幣別記帳。
• 分享/匯出文字同步以警告取代錯誤總額與結算。
• per-expense 個別金額顯示維持正確(各自快照幣別),不受影響。
• 單一幣別行程(常態)行為完全不變。

完整 mixed-currency UX(按幣別分組 vs 換算成 base currency)為產品決策,Codex 已列為待拍板,本 PR 先止血避免顯示錯誤數字。

驗證

• split-meow typecheck ✓ · vitest HomeAndHistorySmoke 19 tests(含 2 新混幣/單幣測試)✓
• changeset @app/split-meow patch

🤖 Generated with Claude Code

[github-actions]

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Dependency Review

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

Scanned Files

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