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

drivers/char/keyboard.c

@@ -1,8 +1,6 @@
 #include <drivers/keyboard.h>
 #include <drivers/tty.h>
-#include <arch/x86_64/isr.h>
-#include <arch/x86_64/pic.h>
-#include <arch/x86_64/io.h>
+#include <arch/arch.h>
 
 #define KEYBOARD_DATA_PORT    0x60
 #define KEYBOARD_STATUS_PORT  0x64
@@ -44,6 +42,7 @@ static void buffer_enqueue(uint16_t key) {
     }
 }
 
+#if defined(__x86_64__)
 static void keyboard_interrupt_handler(registers_t* regs) {
     (void)regs;
     uint8_t scancode = inb(KEYBOARD_DATA_PORT);
@@ -112,23 +111,40 @@ static void keyboard_interrupt_handler(registers_t* regs) {
         buffer_enqueue((uint16_t)c);
     }
 }
+#endif
 
 void keyboard_init(void) {
     buffer_head = 0;
     buffer_tail = 0;
 
+#if defined(__x86_64__)
     isr_register_handler(33, keyboard_interrupt_handler); // IRQ1
     pic_clear_mask(1);
+#endif
 }
 
+#if defined(__aarch64__)
+#include <arch/aarch64/uart.h>
+#endif
+
 bool keyboard_has_key(void) {
+#if defined(__aarch64__)
+    if (uart_pl011_has_data()) return true;
+#endif
     return buffer_head != buffer_tail;
 }
 
 uint16_t keyboard_get_key(void) {
     while (!keyboard_has_key()) {
-        hlt();
+        arch_halt();
     }
+#if defined(__aarch64__)
+    if (uart_pl011_has_data()) {
+        char c = uart_pl011_getc();
+        if (c == '\r') c = '\n';
+        return (uint16_t)(uint8_t)c;
+    }
+#endif
     uint16_t key = key_buffer[buffer_tail];
     buffer_tail = (buffer_tail + 1) % KEYBOARD_BUFFER_SIZE;
     return key;

drivers/char/tty.c

@@ -12,16 +12,17 @@ typedef struct {
 static tty_t ttys[MAX_TTYS];
 static int current_tty = 0;
 
-static volatile uint16_t* const VGA_MEM = (uint16_t*)VGA_MEMORY;
-
 static void tty_render_current(void) {
+#if defined(__x86_64__)
+    volatile uint16_t* const vga_mem = (uint16_t*)VGA_MEMORY;
     tty_t* t = &ttys[current_tty];
     for (int y = 0; y < TTY_HEIGHT; y++) {
         for (int x = 0; x < TTY_WIDTH; x++) {
-            VGA_MEM[y * TTY_WIDTH + x] = t->buffer[y][x];
+            vga_mem[y * TTY_WIDTH + x] = t->buffer[y][x];
         }
     }
     vga_set_cursor(t->cursor_row, t->cursor_col);
+#endif
 }
 
 void tty_switch(int index) {
@@ -62,7 +63,9 @@ void tty_set_cursor(int row, int col) {
     tty_t* t = &ttys[current_tty];
     t->cursor_row = row;
     t->cursor_col = col;
+#if defined(__x86_64__)
     vga_set_cursor(row, col);
+#endif
 }
 
 void tty_write(const char* data, size_t size) {
@@ -150,7 +153,9 @@ void tty_write_string(const char* data) {
 }
 
 void tty_init(void) {
+#if defined(__x86_64__)
     vga_init();
+#endif
     for (int i = 0; i < MAX_TTYS; i++) {
         ttys[i].cursor_row = 0;
         ttys[i].cursor_col = 0;