Completes FN-5481 by unskipping soft-delete matrix backstop tests, adding substantial new coverage to the soft-delete end-to-end test suite (290 lines added/modified) and updating the verification matrix documentation to reflect the newly enabled test scenarios.
Fusion-Task-Id: FN-5481
Implement the hard-archived delete contract: add a typed `ArchivedTaskDeleteError`, map hard-archived task deletes to HTTP 410 Gone at both the store and routes layers, and document the invariant in the soft-delete verification matrix.
Fusion-Task-Id: FN-5196
Completes FN-5153 by delivering the soft-delete verification gate with a new end-to-end test suite covering the full soft-delete lifecycle and a documentation matrix summarizing the gate behavior. Updates the dashboard test file and adds a brief entry to AGENTS.md to surface the new feature.
Fusion-Task-Id: FN-5153
