feat(rust): Implement Rust-for-SUB-OS kernel layer, ChaCha20 crypto, HWMON thermal governor, and lazybox applets

- Add freestanding no_std Rust kernel layer compiled with rustc
- Implement memory-safe ChaCha20 RFC-8439 stream cipher and CSPRNG in Rust
- Implement intelligent thermal fan speed governor in Rust
- Add printk macro bridge (kprint!, kprintln!) for Rust
- Register 'rustinfo' and 'chacha20' LazyBox applets
- Enable x86_64 hardware FPU & SSE (CR4.OSFXSR/OSXMMEXCPT)
- Add cross-architecture C-bridge for ARM targets
- Update stage2.asm kernel sector copy bounds to 448 KB

arch/x86_64/cpu/arch.c

@@ -7,11 +7,24 @@
 #include <arch/x86_64/cpuid.h>
 #include <kernel/timer.h>
 
+static void enable_fpu_sse(void) {
+    uint64_t cr0, cr4;
+    __asm__ volatile ("mov %%cr0, %0" : "=r"(cr0));
+    cr0 &= ~(1ULL << 2); // Clear EM (x87 emulation)
+    cr0 |= (1ULL << 1);  // Set MP (Monitor co-processor)
+    __asm__ volatile ("mov %0, %%cr0" :: "r"(cr0));
+
+    __asm__ volatile ("mov %%cr4, %0" : "=r"(cr4));
+    cr4 |= (1ULL << 9) | (1ULL << 10); // Set OSFXSR (bit 9) and OSXMMEXCPT (bit 10)
+    __asm__ volatile ("mov %0, %%cr4" :: "r"(cr4));
+}
+
 void arch_early_init(void) {
     // x86_64 serial and tty initialized in main
 }
 
 void arch_init(void) {
+    enable_fpu_sse();
     gdt_init();
     idt_init();
     isr_init();