Fix EPM active sprint story rollups

[Juce-me]

Summary

• Trust Jira sprint-filtered child rollup query results when building active EPM project hierarchies.
• Preserve existing initiative-root active rollup filtering and backlog filtering behavior.
• Add regression coverage for stories returned by a sprint-filtered child query without a sprint field in the response payload.

Validation

• python -m unittest discover -s tests passed: 883 tests, 1 skipped.
• git diff --check passed.

Notes

• No frontend source changed, so no frontend build or screenshots were needed.