⚡ Bolt: [performance improvement] Batched artifact fetching in board hooks

[Donach]

💡 What: Added findManyByIds to ArtifactRepository using a batched inArray query instead of querying each artifact individually inside the FeathersJS hook loops, and refactored the hooks to create an intermediate artifact mapping.
🎯 Why: FeathersJS board hooks evaluate nested board.objects relationships. Previously, when multiple objects pointed to an artifact, each lookup triggered a separate findById resulting in an N+1 query issue.
📊 Impact: Considerably reduces database roundtrips during any multi-object board payload resolution. Lookups are condensed into one batched database operation.
🔬 Measurement: Verify by executing board hook queries with multiple internal artifact references. Test suites continue to pass correctly, reflecting the preservation of functionality with improved performance.

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PR created automatically by Jules for task 2747807462789992934 started by @Donach

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