feat(reports): add backtest report library

[LemonCANDY42]

Summary

Add a dedicated /reports Backtest Report Library page.

This follows the product shape discussed in #216:

• dedicated Reports route, not a Home section
• lists recent runs with backtest metrics/report output
• row fields include run id, status, created time, truncated prompt, symbols, date range, return, Sharpe, and links to Run Detail + Compare
• search covers run id, prompt, symbol, and status
• v1 filters cover status and created-date range
• sorting defaults to newest first, with options for oldest, return, and Sharpe
• page and sidebar copy are localized in English and zh-CN

This remains draft because #216 was explicitly sequenced after #214 and #215.

Validation

• npm test -- --run src/pages/__tests__/Reports.test.tsx
• npm run build
• git diff --check

Refs #216.

[LemonCANDY42]

Ready for review now.

Updated this branch on top of current upstream/main and resolved the frontend/src/lib/api.ts conflict by keeping the opt-in Run Detail getRun(id, params) contract from #225 while preserving listRuns(limit) for the Reports Library scan.

I also tightened Reports.test.tsx so it explicitly covers the #216 acceptance points: listing report runs, Full Report links, and search filtering.

Validation:

• npm test -- --run src/pages/__tests__/Reports.test.tsx
• npm run build
• git diff --check
• NODE_OPTIONS="--localstorage-file=/tmp/vibe-vitest-localstorage.json" npm test -- --run

[warren618]

Merged 🎉 Thanks @LemonCANDY42 — this matches the product shape we agreed in #216 (dedicated /reports Run Library page, the row fields + search/filter scope, deferring multi-select compare to a follow-up). Open-box verified before merge: npm run build is clean and the full vitest suite passes 209/209, including the new Reports.test.tsx covering listing, the Full Report link, and search filtering. The listRuns(limit?) change lines up with the existing GET /runs?limit backend contract. Closes #216.