Apply ChatGPT's FileBox method_id fixes and add build scripts

- Add plugin host initialization for LLVM mode (fixes method_id injection)
- Add FileBox method_id injection test
- Enhance MIR14 stability test
- Add warning for Mock LLVM implementation
- Create build scripts for JIT/LLVM with proper settings (24 threads, timeout)
- Update CLAUDE.md with build instructions and FileBox test results

Note: FileBox file I/O still not working in LLVM execution (separate issue)

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

tests/mir_instruction_set_sync.rs

@@ -1,8 +1,9 @@
 use nyash_rust::mir::instruction_introspection;
 
-// MIR14: ensure instruction count stays fixed at 14
+// MIR14: ensure instruction roster remains stable
 #[test]
-fn mir14_instruction_count() {
+fn mir14_shape_is_fixed() {
     let impl_names = instruction_introspection::mir14_instruction_names();
     assert_eq!(impl_names.len(), 14, "MIR14 must contain exactly 14 instructions");
+    assert!(impl_names.contains(&"UnaryOp"), "MIR14 must include UnaryOp");
 }