WCIF v1.1: support Best-of-5 (format '5') rounds (3BLD change)

WCIF spec recently moved to v1.1 (notably: 3x3 Blindfolded is now **Best of 5**).

DelegateDashboard has its own round format mapping in `src/lib/domain/events.ts`:
- `roundFormats` includes a/ m /3/2/1 but **does not include format id `5`**.
- Downstream, `roundFormatById()` is used in `src/lib/wcif/persons.ts` and elsewhere to decide whether to read `result.average` vs `result.best`.
- With WCIF v1.1 competitions, any round with `format: "5"` (Best of 5) will cause `roundFormatById()` to return undefined, which breaks seed/result lookups and likely some UI/exports.

Reference: thewca/wca-helpers PR “Wcif 1.1 updates” explicitly calls out “3bld is now best of 5” and updates their RoundFormat handling:
https://github.com/thewca/wca-helpers/pull/47

## Acceptance criteria
- Add round format `id: "5"` with appropriate labels (e.g., short `bo5`, long `Best of 5`, rankingResult `single`).
- Add/update unit tests in `src/lib/domain/events.test.ts` (and any others) to cover `roundFormatById("5")` and `roundFormatShortById("5")`.
- Verify any logic that depends on format IDs still works (seed results, result rendering, import/export, validation).

## Nice to have
- Audit other WCIF-v1.1-related changes (if any) and update mocks in wcif tests to use `formatVersion: "1.1"` where relevant.

src/lib/domain/events.ts から始め、src/lib/wcif/persons.ts にある roundFormatById() の利用箇所を調べます。src/lib/domain/events.test.ts のテストを実行し、その後、フォーマット "5" の seed/result ルックアップ、レンダリング、インポート/エクスポート、バリデーションを確認します。既存のフォーマットを壊さずに Best-of-5 がマッピングされ、カバーされていれば完了です。

索引モデルが issue の本文から書いたものです。