♻️(search) migrate to opensearch-py Q-types

[StephanMeijer]

Important

Please merge first: #129, #127, #126, #125, #124, #123, #138

Important

Moved to #139

Summary

• Refactor search.py to use Q objects from opensearch-py for type-safe query building
• Add SortSpec dataclass for DSL-like sort clause construction
• Add comprehensive test suite (84 tests total: 53 unit + 31 integration)
• Remove all typing.Any usage in favor of proper types

Changes

File	Description
src/backend/core/services/search.py	Migrated to Q objects, added SortSpec
src/backend/core/views.py	Deletion query migrated to Q objects
src/backend/core/tests/test_search.py	53 new unit tests
src/backend/core/tests/test_api_search.py	13 new integration tests
src/backend/core/tests/test_api_documents_delete.py	18 deletion tests

Verification

• ✅ All 84 tests passing
• ✅ 100% behavioral equivalence maintained
• ✅ Access control logic preserved (security critical)
• ✅ No changes to indexing.py, schemas, or script_fields

[Copilot]

Pull request overview

This PR refactors the backend OpenSearch query-building layer to use opensearch-py Q objects (instead of raw dicts), adds a small sort DSL wrapper, and introduces a broad set of unit/integration tests to lock in access-control and query-shape behavior.

Changes:

• Migrated search query construction (get_filter, get_query, get_full_text_query) to opensearchpy.Q and introduced SortSpec for sort clause generation.
• Updated the document deletion query builder to use Q objects and serialize via .to_dict().
• Added extensive unit + API integration test coverage for query building, access control, filtering, sorting, and deletion behavior.

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
src/backend/core/services/search.py	Rebuilds search/filter/query/sort composition using opensearchpy.Q and SortSpec, serializing to dict at request time.
src/backend/core/views.py	Updates deletion query construction to build with Q objects and serialize to dict for OpenSearch.
src/backend/core/tests/test_search.py	Adds a large unit test suite for query building, access control filtering, and sort spec behavior.
src/backend/core/tests/test_api_search.py	Adds integration tests for the search API endpoint (auth, filtering, sorting, access control).
src/backend/core/tests/test_api_documents_delete.py	Adds deletion-query unit tests alongside existing deletion endpoint integration tests.

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[StephanMeijer]

Important

Moved to #139