Implement GDT and basic IDT setup

This commit adds GDT initialization with proper code/data segments and reloads CS.

It also adds the initial IDT structure and loads an empty IDT.

Build configuration updated to disable SSE/MMX to prevent compiler generation of unsupported instructions in early boot.

.gitignore

@@ -5,3 +5,5 @@ release/
 debug_grub/
 *_output.txt
 snippet.*
+qemu.log
+iso_output.txt