Feat/1222 add experiment metric indexes

[Peolite001]

Summary

Closes #1222

Adds database indexes to the experiment_metrics table to prevent sequential scans as the table grows. Both entity-level @Index decorators and a corresponding migration are included so existing databases are updated via a reviewable migration.

Changes

src/ab-testing/entities/experiment-metric.entity.ts

• Imported Index from typeorm
• Added four @Index decorators to the entity class:

Index	Column(s)	Rationale
IDX_experiment_metrics_experiment_id	experimentId	Foreign key used in every JOIN when loading the experiment.metrics relation
IDX_experiment_metrics_type	type	Filtering/grouping metrics by metric type
IDX_experiment_metrics_created_at	createdAt	ORDER BY createdAt DESC in list queries
IDX_experiment_metrics_experiment_is_primary	experimentId, isPrimary	Composite index for "get primary metric(s) for a given experiment"

src/migrations/1801000000000-add-experiment-metric-indexes.ts (new)

• Creates the same four indexes using queryRunner.createIndices
• down() drops them in reverse order for clean rollback

Checklist

• Entity carries indexes covering common lookup/foreign-key columns
• Migration creates the indexes and runs cleanly on an existing database
• No duplicate/redundant indexes introduced
• down() migration cleanly rolls back all indexes

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[RUKAYAT-CODER]

Well done on the job done so far!
Kindly fix workflow to pass

[Peolite001]

Well done on the job done so far! Kindly fix workflow to pass

done

[RUKAYAT-CODER]

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