Store per-fault severity in PendingCluster for accurate HIGHEST_SEVERITY representative reassignment

[eclipse0922]

Context

In CorrelationEngine::process_clear(), when a fault that is the representative of a pending cluster is cleared, the representative must be reassigned. For FIRST and MOST_RECENT policies this works correctly, but for HIGHEST_SEVERITY the reassignment falls back to codes.front() because PendingCluster does not store individual fault severities.

Current behavior

case Representative::HIGHEST_SEVERITY:
  // fall back to first remaining fault
  pending_cluster.representative_code = codes.front();

Expected behavior

Store per-fault severity in PendingCluster (e.g., std::map<std::string, std::string> fault_severities) so that the highest-severity fault can be accurately selected as the new representative.

Notes

Identified during review of #211 by @mfaferek93.