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

kernel/task.c

@@ -2,6 +2,7 @@
 #include <kernel/sched.h>
 #include <mm/kmalloc.h>
 #include <lib/string.h>
+#include <arch/arch.h>
 
 static pid_t next_pid = 1;
 static task_t* current_task = NULL;
@@ -55,7 +56,7 @@ void task_exit(int exit_code) {
         sched_yield();
     }
     while (1) {
-        __asm__ volatile("hlt");
+        arch_halt();
     }
 }