Add game field to reactions for efficient Constellation queries
- Add required "game" field to reaction lexicon
- Update ReactionRecord type with game field
- Refactor fetchGameReactions to query by game URI instead of
individual move URIs (single Constellation query vs N queries)
- Group reactions by move URI client-side
- Update reaction API endpoint to include game field
- Update game page to use new reaction fetching approach
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>