feat(arch): Add AArch64 / ARMv8i CPU support, cross-compilation & Linux Kconfig TUI

- Implement AArch64 HAL, vector table (16 aligned vectors), GICv2, Generic Timer, Stage-1 MMU (39-bit VA), PL011 UART
- Build unified multi-architecture abstraction layer in include/arch/arch.h
- Create interactive Linux-like Kconfig TUI menuconfig in scripts/kconfig/menuconfig.py
- Support make menuconfig, defconfig, x86_64_defconfig, aarch64_defconfig
- Update master Makefile for cross-compiling x86_64 (x86_64-elf-) and AArch64 (aarch64-linux-gnu-)
- Dynamic architecture awareness across printk, uname, neofetch, and LazyBox

userland/lazybox/lazybox.c

@@ -28,9 +28,7 @@
 #include <ipc/ipc.h>
 #include <mm/pmm.h>
 #include <mm/kmalloc.h>
-#include <arch/x86_64/pit.h>
-#include <arch/x86_64/cpuid.h>
-#include <arch/x86_64/io.h>
+#include <arch/arch.h>
 #include <kernel/printk.h>
 #include <lib/string.h>
 #include <lib/printf.h>
@@ -662,7 +660,7 @@ static int applet_mouse(int argc, char** argv) {
 
 static int applet_uname(int argc, char** argv) {
     if (argc >= 2 && strcmp(argv[1], "-a") == 0) {
-        printk("SUB-OS sub-node %s #1 SMP PREEMPT Sun Aug 16 2026 x86_64 GNU/LazyBox\n", kernel_get_version());
+        printk("SUB-OS sub-node %s #1 SMP PREEMPT 2026 %s GNU/LazyBox\n", kernel_get_version(), arch_get_name());
     } else {
         printk("SUB-OS\n");
     }