fix(userland): Fix 'clear' command, backspace keycodes (0x7F/0x08), serial keyboard input & make run target

- Add 'clear' and 'cls' builtin handlers in LazyBox shell
- Output ANSI \033[2J\033[H sequence on tty_clear() to clear serial/UART terminals
- Support both ASCII 0x7F (DEL) and 0x08 (BS) for Backspace in shell and nano editor
- Connect 16550 serial input to keyboard_get_key() on x86_64 for headless terminals
- Add ANSI escape sequence decoding for arrow keys (Up/Down/Left/Right/Home/End/Del)
- Update Makefile 'make run' and 'make qemu' with -display none for smooth terminal execution
- Add 'make run-gui' target for optional graphical SDL/GTK window

kernel/main.c

@@ -195,9 +195,6 @@ static void subos_modular_core_boot(void) {
     printk(ANSI_BRIGHT_GREEN "ACTIVE\n" ANSI_RESET);
 
     // Launch Shell
-#if defined(__x86_64__)
-    tty_clear();
-#endif
     shell_run();
 
     while (1) {