[Backend] — Scoreline predictions & points-based grading (1 / 3 / 4 points)

[Olowodarey]

Background

`src/matches/entities/match-prediction.entity.

Goal

Store the predicted scoreline, compute points_earned per prediction using
the 1/3/4-point rules (multiplied by points_multiplier), and keep
is_correct as a derived "result was correct" flag for backwards
compatibility with existing consumers (getUserScore, ParticipantWithStats).

Tasks

1. Entity changes (src/matches/entities/match-prediction.entity.ts):
   derived/denormalized column for now — set it from the predicted
2. Migration: <timestamp>-AddScorelineAndPointsToMatchPrediction.ts —
3. Indexer — extractEventData() 'PredictionSubmitted' case: add
4. Indexer — handlePredictionSubmitted():
   • persist predicted_home_score / predicted_away_score from the event
   • derive predicted_outcome from the scoreline:
   • replace the current strict validation against a predicted_outcome

Acceptance Criteria

• match_predictions table has predicted_home_score,
• calculatePredictionPoints returns 4 for an exact-score correct
• handleMatchResultSubmitted() grades all predictions for a match and
• GET /creator-events/:id/score/:address includes totalPoints and