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

userland/lazybox/nano.c

@@ -287,7 +287,8 @@ int nano_main(int argc, char** argv) {
                 }
                 break;
 
-            case '\b': // Backspace
+            case '\b': // Backspace (0x08)
+            case 0x7F: // DEL
                 if (nano_cursor_col > 0) {
                     memmove(&nano_lines[nano_cursor_row][nano_cursor_col - 1],
                             &nano_lines[nano_cursor_row][nano_cursor_col],