fix: remove task-continuation-enforcer references after dev merge

Dev removed task-continuation-enforcer entirely. Remove all remaining
references from plugin hooks, event handler, tool-execute-before, and
config schema to align with origin/dev.

src/plugin/tool-execute-before.ts

@@ -88,7 +88,6 @@ export function createToolExecuteBeforeHandler(args: {
       if (command === "stop-continuation" && sessionID) {
         hooks.stopContinuationGuard?.stop(sessionID)
         hooks.todoContinuationEnforcer?.cancelAllCountdowns()
-        hooks.taskContinuationEnforcer?.cancelAllCountdowns()
         hooks.ralphLoop?.cancelLoop(sessionID)
         clearBoulderState(ctx.directory)
         log("[stop-continuation] All continuation mechanisms stopped", {