Adds a reconcile script to recover leaked soft-deleted tasks, threads delete audit context through all callers, and records soft-delete audit events with archive column tracking across core/engine/cli/dashboard, with reliability backstop tests covering caller alignment.
Fusion-Task-Id: FN-5175
Adds a `lineage-unlink` flag to triage parent deletes (FN-5131), enabling the split-into-subtasks path to break parent-child lineage on deletion. The primary addition is a comprehensive new test covering that split scenario, with minor adjustments to two existing lineage-related test files.
Fusion-Task-Id: FN-5131
Fusion-Task-Lineage: cb720e8f-8c49-42e4-873a-9949f3ba3427
