Changed event handler to:
- Listen to 'cdc.contribution.outbox' topic (CDC/Debezium format)
- Handle 'ContributionAccountUpdated' events instead of 'ContributionCalculated'
- Use effectiveContribution for mining power calculation
This fixes the issue where mining accounts had zero totalContribution
because they weren't receiving contribution sync events.
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>