v5.3.0 - Login System

Boot animation (NyxOS-themed, ~5s, 23-step progress bar)
Auth backend: credential storage on EXT2 (/etc/passwd)
Login screen: framebuffer UI with keyboard input (no mouse)
Default user nyx/nyx with fallback when no EXT2 disk
On login failure → reboot; on success → launch NyxOS Desktop
Keyboard buffer exposed for direct polling