fix: QA issues — composite index, anchors, fallbacks

- Add composite index ix_translation_records_run_source_hash
  for NOT EXISTS dedup subquery performance + Alembic migration
- Remove duplicate #endregion in orchestrator.py (INV_3)
- Replace hardcoded RU fallback 'Статус' with 'Status'
- Add early return guard to loadMoreRecords()
- Show records summary always when recordsTotal > 0

backend/src/plugins/translate/orchestrator.py

@@ -173,4 +173,3 @@ class TranslationOrchestrator:
     # endregion get_run_history
 
 # #endregion TranslationOrchestrator
-# #endregion TranslationOrchestrator