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

arch/x86_64/configs/defconfig

@@ -0,0 +1,45 @@
+#
+# Automatically generated by SUB-OS Kconfig for x86_64
+#
+CONFIG_ARCH=x86_64
+CONFIG_ARCH_X86_64=y
+CONFIG_BPF_VM=y
+CONFIG_DRV_AHCI=y
+CONFIG_DRV_ATA=y
+CONFIG_DRV_BOCHS_VBE=y
+CONFIG_DRV_CANVAS_2D=y
+CONFIG_DRV_E1000=y
+CONFIG_DRV_HWMON=y
+CONFIG_DRV_NVME=y
+CONFIG_DRV_PTY=y
+CONFIG_DRV_RAMDISK=y
+CONFIG_DRV_RTL8139=y
+CONFIG_DRV_SOUND_AC97=y
+CONFIG_DRV_SOUND_HDA=y
+CONFIG_DRV_USB_XHCI=y
+CONFIG_DRV_VIRTIO_BLK=y
+CONFIG_DRV_VIRTIO_NET=y
+CONFIG_DRV_VIRTIO_RNG=y
+CONFIG_FS_DEVFS=y
+CONFIG_FS_EXT2=y
+CONFIG_FS_FAT32=y
+CONFIG_FS_PROCFS=y
+CONFIG_FS_RAMFS=y
+CONFIG_FS_SYSFS=y
+CONFIG_FS_VFS=y
+CONFIG_IO_URING=y
+CONFIG_MM_PMM=y
+CONFIG_MM_SLAB=y
+CONFIG_MM_VMA=y
+CONFIG_NET_FILTER=y
+CONFIG_NET_HTTPD=y
+CONFIG_NET_SSHD=y
+CONFIG_NET_STACK=y
+CONFIG_OPTIMIZATION="-O2"
+CONFIG_PREEMPT=y
+CONFIG_SECURITY_KEYRING=y
+CONFIG_SECURITY_LSM=y
+CONFIG_SMP=y
+CONFIG_SUBOS_HOSTNAME="sub-os"
+CONFIG_SUBOS_VERSION="0.2.0-lts"
+CONFIG_USERLAND_LAZYBOX=y

arch/x86_64/cpu/arch.c

@@ -0,0 +1,32 @@
+#include <arch/arch.h>
+#include <arch/x86_64/gdt.h>
+#include <arch/x86_64/idt.h>
+#include <arch/x86_64/isr.h>
+#include <arch/x86_64/pic.h>
+#include <arch/x86_64/pit.h>
+#include <arch/x86_64/cpuid.h>
+#include <kernel/timer.h>
+
+void arch_early_init(void) {
+    // x86_64 serial and tty initialized in main
+}
+
+void arch_init(void) {
+    gdt_init();
+    idt_init();
+    isr_init();
+    pic_init();
+    pit_init(100);
+    timer_wheel_init();
+    arch_enable_interrupts();
+}
+
+const char* arch_get_name(void) {
+    return "x86_64 (AMD64)";
+}
+
+uint32_t arch_get_cpu_id(void) {
+    uint32_t eax = 0, ebx = 0, ecx = 0, edx = 0;
+    cpuid(1, &eax, &ebx, &ecx, &edx);
+    return (ebx >> 24) & 0xFF;
+}