feat: Phase 2.4 NyRT→NyKernel Architecture Revolution 100%完了！

ChatGPT5 Pro設計分析による42%コード削減の完全実現：
- crates/nyrt → crates/nyash_kernel 完全移行
- with_legacy_vm_args系統11箇所削除（encode/birth/future/invoke系）
- Plugin-First Architecture統一（VM依存根絶）
- libnyash_kernel.a生成成功（0エラー・0警告）
- LLVM統合更新（build_llvm.sh, ny-llvmc対応）

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

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

crates/nyash_kernel/src/plugin/semantics.rs

@@ -0,0 +1,47 @@
+// ---- Unified semantics shims (handle-based) ----
+// Exported as: nyash.semantics.add_hh(i64 lhs_handle, i64 rhs_handle) -> i64 (NyashBox handle)
+#[export_name = "nyash.semantics.add_hh"]
+pub extern "C" fn nyash_semantics_add_hh_export(lhs_h: i64, rhs_h: i64) -> i64 {
+    use nyash_rust::jit::rt::handles;
+    use nyash_rust::{
+        box_trait::{IntegerBox, StringBox},
+        runtime::semantics,
+    };
+    if lhs_h <= 0 || rhs_h <= 0 {
+        return 0;
+    }
+    let lhs = if let Some(obj) = handles::get(lhs_h) {
+        obj
+    } else {
+        return 0;
+    };
+    let rhs = if let Some(obj) = handles::get(rhs_h) {
+        obj
+    } else {
+        return 0;
+    };
+    let ls_opt = semantics::coerce_to_string(lhs.as_ref());
+    let rs_opt = semantics::coerce_to_string(rhs.as_ref());
+    if ls_opt.is_some() || rs_opt.is_some() {
+        let ls = ls_opt.unwrap_or_else(|| lhs.to_string_box().value);
+        let rs = rs_opt.unwrap_or_else(|| rhs.to_string_box().value);
+        let s = format!("{}{}", ls, rs);
+        let arc: std::sync::Arc<dyn nyash_rust::box_trait::NyashBox> =
+            std::sync::Arc::new(StringBox::new(s));
+        return handles::to_handle(arc) as i64;
+    }
+    if let (Some(li), Some(ri)) = (
+        semantics::coerce_to_i64(lhs.as_ref()),
+        semantics::coerce_to_i64(rhs.as_ref()),
+    ) {
+        let arc: std::sync::Arc<dyn nyash_rust::box_trait::NyashBox> =
+            std::sync::Arc::new(IntegerBox::new(li + ri));
+        return handles::to_handle(arc) as i64;
+    }
+    // Fallback: stringify both and concat to preserve total order
+    let ls = lhs.to_string_box().value;
+    let rs = rhs.to_string_box().value;
+    let arc: std::sync::Arc<dyn nyash_rust::box_trait::NyashBox> =
+        std::sync::Arc::new(StringBox::new(format!("{}{}", ls, rs)));
+    handles::to_handle(arc) as i64
+}