fix(workflows): minimal-invasive auto-detect integration from project config

- Add _INTEGRATION_JSON local constant in engine.py
- Replace post-processing _resolve_integration_auto() with inline
  _resolve_default() + _load_project_integration() methods
- Revert all Black style-only changes to engine.py, __init__.py
- Delete unnecessary constants.py
- Add TestIntegrationAutoDetect with 6 tests (no changes to existing tests)
- Update workflow.yml: default 'auto', remove static integrations.any list

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Co-authored-by: markuswondrak <245696895+markuswondrak@users.noreply.github.com>

Author: Copilot