#1003 SwitchOperator runs every case: case tasks are ordinary graph tasks (auto-chained before the switch) and only the head of an unselected case is skipped

EARS: When a SwitchOperator selects a case, the Highway engine shall run only that case's task and the tasks chained after it, skip every other case's task and its chain, and run the switch's dependents after the selected case has finished. Case tasks shall never run from the graph before the switch. Found while extending #974 (lead request). The DSL prompt's switch example defines the case tasks before the switch; the builder auto-chains them (handle_json deps [classify], handle_csv deps [handle_json], ...), so they become ordinary graph tasks that run before the switch decides. control_flow.execute_switch_operator marks only the unselected case ids executed, so a task chained after an unselected case still runs.