WS-A.4: flip deadcode gate to blocking; delete 3 dead leftovers

[LukasWodka]

Part of epic tracebloc/backend#1106. Full spec: report §5 (mirrored on the epic; artifact https://claude.ai/code/artifact/b4b6e6a6-4d76-4e46-a668-6f4f0f944344). WS-A.4: delete config.clearAll, push.allCategoryIDs, submit.isSubmitError (#127 leftovers); allowlist 2 Stringers + 2 parity harnesses; remove continue-on-error from the deadcode CI step. Exit: deadcode blocking with clean run.

[LukasWodka]

Shipped in #313 (merged to develop). Closing as completed — CLI refactor epic backend#1106 cleanup.