refactor(query): extract query pipeline mutation logic to reduce complexity

[SaitejaKommi]

Summary

This PR reduces the excessive complexity in query.py by separating query pipeline mutation logic from lower-level Elasticsearch object creation responsibilities.

The refactor improves modular boundaries by moving parsing and tree transformation behavior into a dedicated pipeline module, while keeping runtime behavior fully preserved.

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Related Issue

Fixes #393

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What Changed

• Created query_pipeline.py to encapsulate parsing and tree mutation workflow
• Moved pipeline responsibilities such as:
  • compute_facets_filters
  • resolve_unknown_operation
  • check_query
  • parse_query
• Simplified query.py to focus on orchestration and execution flow
• Kept query.py as the bridge between pipeline processing and ElasticsearchQueryBuilder
• Preserved existing behavior with no intended logic changes

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Affected Files

• query.py
• query_pipeline.py

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Testing

Verification gateway executed successfully:

• Backend unit tests ✅
• Backend integration tests (Elasticsearch verified context) ✅
• Frontend component tests ✅

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Notes

This is a structural refactor focused on reducing complexity and improving maintainability through clearer separation of concerns.