Two fixes introduced by the non-null assertion cleanup produced type
errors:
- scoring-event.ts: `?? ""` was wrong type for a participant object map;
restructured to explicit null guards so TypeScript can narrow correctly
- standings-sync/index.ts: `?? null` after name-match lookup lost the
truthy guarantee, causing TS18047 on the write-back block; added
`participant &&` guard before accessing its properties
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
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