fix(page-fault): remove redundant CR2 read that panics on error

The page fault handler was reading CR2 twice:
1. Line 894: Cr2::read().unwrap_or(...) - handles errors gracefully
2. Line 923: Cr2::read().expect(...) - panics on error

The second read is redundant and uses .expect() which causes panics
when CR2::read() returns Err. This was causing CI failures at
[80/138] SIGTERM kill test with KERNEL PANIC at interrupts.rs:923:37.

Fix: Reuse the cr2 value already read safely on line 894 by converting
it back to a VirtAddr instead of reading CR2 again.

Co-Authored-By: Ryan Breen <ryanbreen@gmail.com>
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: 3 people

kernel/src/interrupts.rs

@@ -920,7 +920,8 @@ extern "x86-interrupt" fn page_fault_handler(
     // Increment preempt count on exception entry FIRST to avoid recursion
     crate::per_cpu::preempt_disable();
 
-    let accessed_addr = Cr2::read().expect("Failed to read accessed address from CR2");
+    // Use the cr2 value we already read safely above (line 894)
+    let accessed_addr = x86_64::VirtAddr::new(cr2);
 
     // Skip raw serial output for potential CoW faults
     if !is_potential_cow {