Initial commit: XOmB exokernel foundation

Core kernel infrastructure:
- Multiboot2 boot with GRUB, long mode setup, higher-half kernel
- Serial port output for debugging
- Unified boot info abstraction for future UEFI support

Memory management:
- Physical frame allocator with bitmap tracking
- Page table manipulation via recursive mapping (PML4[510])
- Support for 4KB, 2MB, and 1GB page mappings
- TLB invalidation and proper NXE support

Build system:
- Cargo-based build with custom x86_64 target
- Makefile for QEMU and Bochs testing
- GRUB ISO generation for multiboot2 boot

src/multiboot2_main.rs

@@ -0,0 +1,31 @@
+//! XOmB Multiboot2 Entry Point
+//!
+//! This is the Rust entry point for multiboot2 boot (used by Bochs/GRUB).
+//! The actual entry is in assembly (boot/multiboot2_header.s), which then
+//! calls into this code.
+
+#![no_std]
+#![no_main]
+
+use core::panic::PanicInfo;
+use core::fmt::Write;
+
+// Re-export the library
+use xomb::serial::SerialPort;
+
+// Pull in the multiboot2 entry point
+pub use xomb::boot::multiboot2::multiboot2_entry;
+
+/// Panic handler for multiboot2 boot
+#[panic_handler]
+fn panic(info: &PanicInfo) -> ! {
+    let mut serial = unsafe { SerialPort::new(0x3F8) };
+    let _ = writeln!(serial, "\n!!! KERNEL PANIC !!!");
+    let _ = writeln!(serial, "{}", info);
+
+    loop {
+        unsafe {
+            core::arch::asm!("cli; hlt", options(nostack, nomem));
+        }
+    }
+}