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/aarch64/cpu/arch.c

@@ -0,0 +1,65 @@
+#include <arch/arch.h>
+#include <arch/aarch64/cpu.h>
+#include <arch/aarch64/gic.h>
+#include <arch/aarch64/timer.h>
+#include <arch/aarch64/uart.h>
+#include <arch/aarch64/mmu.h>
+#include <arch/x86_64/cpuid.h>
+#include <kernel/printk.h>
+#include <lib/string.h>
+
+static cpu_info_t aarch64_compat_cpu;
+
+void arch_early_init(void) {
+    uart_pl011_init();
+}
+
+void arch_init(void) {
+    aarch64_cpu_init();
+    gic_init();
+    aarch64_timer_init(100);
+    aarch64_mmu_init();
+
+    // Populate compatibility CPU info structure for procfs
+    memset(&aarch64_compat_cpu, 0, sizeof(aarch64_compat_cpu));
+    const aarch64_cpu_info_t* info = aarch64_get_cpu_info();
+    strncpy(aarch64_compat_cpu.vendor, "ARM Ltd", sizeof(aarch64_compat_cpu.vendor) - 1);
+    strncpy(aarch64_compat_cpu.model, info->model_name, sizeof(aarch64_compat_cpu.model) - 1);
+    aarch64_compat_cpu.has_fpu = true;
+
+    arch_enable_interrupts();
+}
+
+const char* arch_get_name(void) {
+    return "aarch64 (ARMv8-A)";
+}
+
+uint32_t arch_get_cpu_id(void) {
+    return (uint32_t)(aarch64_get_mpidr() & 0xFF);
+}
+
+// Timer Compatibility Layer for Portable Drivers
+uint64_t pit_get_ticks(void) {
+    return aarch64_timer_get_ticks();
+}
+
+void pit_sleep(uint32_t ms) {
+    uint64_t count = (ms > 10) ? (ms / 10) : 1;
+    uint64_t target = aarch64_timer_get_ticks() + count;
+    while (aarch64_timer_get_ticks() < target) {
+        __asm__ volatile("wfi");
+    }
+}
+
+// Interrupt & CPUID Compatibility Stubs
+void isr_register_handler(uint8_t isr, void* handler) {
+    (void)isr; (void)handler;
+}
+
+void pic_clear_mask(uint8_t irq) {
+    (void)irq;
+}
+
+const cpu_info_t* cpuid_get_info(void) {
+    return &aarch64_compat_cpu;
+}