Include zero-impact imported feedback in impact-sorted results

Description: Include imported feedback with zero or null impact scores in impact-based sorting so these items still appear in results lists and are discoverable. Problem: When sorting by Impact, imported feedback with an impact score of 0 or null is currently excluded from the results. This makes valid feedback disappear from lists and dashboards, hindering discovery, triage, and analysis. Benefit: Including zero/null impact items maintains complete result sets, prevents perceived data loss, supports auditing and trust, and aligns with users’ expectations that a sort operation orders all items rather than filtering some out. It reduces manual workarounds (e.g., re-scoring or separate searches) and creates consistent behavior across UI and API surfaces.