- Rename ERROR_STEPPER_FAULT → ERROR_STEPPER_MOTOR to match main.cpp enum
- Update critical-error predicate to include ERROR_TEMPERATURE_HIGH and
ERROR_WATCHDOG_TIMEOUT (was testing stale pre-fix logic)
- Test 4 now asserts overtemp DOES trigger e-stop (previously asserted opposite)
- Add Test 5 (watchdog triggers e-stop) and Test 6 (memory alloc does not)
- Add ERROR_MEMORY_ALLOC and ERROR_WATCHDOG_TIMEOUT to local enum
- 7 tests, all pass