revert: 古いプラグインシステム実装前の状態に巻き戻し

- ソースコードをcommit 3f7d71fの状態に復元（古いプラグインシステム実装前）
- docsフォルダは最新の状態を維持（BID-FFI設計ドキュメント含む）
- nyashバイナリの基本動作確認済み
- BID-FFIシステムをクリーンに再実装する準備完了

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

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

tests/mir_phase7_async_ops.rs

@@ -107,17 +107,17 @@ fn test_mir_phase7_basic_nowait_await() {
         .flat_map(|block| &block.instructions)
         .collect();
     
-    // Phase 5: FutureNew is deprecated - should contain NewBox "FutureBox" instead
-    let has_future_box = instructions.iter().any(|inst| {
-        matches!(inst, nyash_rust::mir::MirInstruction::NewBox { box_type, .. } if box_type == "FutureBox")
+    // Should contain FutureNew instruction
+    let has_future_new = instructions.iter().any(|inst| {
+        matches!(inst, nyash_rust::mir::MirInstruction::FutureNew { .. })
     });
-    assert!(has_future_box, "MIR should contain NewBox FutureBox instruction");
+    assert!(has_future_new, "MIR should contain FutureNew instruction");
     
-    // Phase 5: Await is deprecated - should contain BoxCall "await" instead
-    let has_await_call = instructions.iter().any(|inst| {
-        matches!(inst, nyash_rust::mir::MirInstruction::BoxCall { method, .. } if method == "await")
+    // Should contain Await instruction
+    let has_await = instructions.iter().any(|inst| {
+        matches!(inst, nyash_rust::mir::MirInstruction::Await { .. })
     });
-    assert!(has_await_call, "MIR should contain BoxCall await instruction");
+    assert!(has_await, "MIR should contain Await instruction");
     
     // Test VM execution
     let mut vm = VM::new();