feat: HAL Device Driver API — driver registry with probe/init/shutdown lifecycle

feat: HAL Device Driver API — driver registry with probe/init/shutdown lifecycle

- Add include/hal/driver.h: struct hal_driver with type, priority, ops (probe/init/shutdown)
- Add src/kernel/driver.c: driver registry with hal_driver_register(), hal_drivers_init_all(),
  hal_drivers_shutdown_all(), hal_driver_find(), hal_driver_count()
- Drivers init in priority order (insertion sort), shutdown in reverse
- HAL_MAX_DRIVERS=32, 6 driver types: PLATFORM, CHAR, BLOCK, NET, DISPLAY, BUS
- Framework ready for existing drivers to self-register (incremental migration)

20/20 smoke, cppcheck clean