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

rust-toolchain.toml

@@ -0,0 +1,13 @@
+[toolchain]
+channel = "nightly"
+components = [
+    "rust-src",
+    "rustfmt",
+    "clippy",
+    "llvm-tools-preview",
+]
+targets = [
+    "x86_64-unknown-uefi",
+    "x86_64-unknown-linux-gnu",  # For host-side unit tests
+]
+profile = "minimal"