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>

src/interpreter/expressions/calls.rs

@@ -13,8 +13,6 @@ use crate::instance::InstanceBox;
 use crate::channel_box::ChannelBox;
 use crate::interpreter::core::{NyashInterpreter, RuntimeError};
 use crate::interpreter::finalization;
-#[cfg(feature = "dynamic-file")]
-use crate::interpreter::plugin_loader::FileBoxProxy;
 use std::sync::Arc;
 
 impl NyashInterpreter {
@@ -257,18 +255,6 @@ impl NyashInterpreter {
             return self.execute_file_method(file_box, method, arguments);
         }
         
-        // FileBoxProxy method calls (動的ライブラリ版)
-        #[cfg(feature = "dynamic-file")]
-        {
-            eprintln!("🔍 DEBUG: Checking if object is FileBoxProxy, type_name: {}", obj_value.type_name());
-            if let Some(file_proxy) = obj_value.as_any().downcast_ref::<crate::interpreter::plugin_loader::FileBoxProxy>() {
-                eprintln!("✅ DEBUG: Object is FileBoxProxy, calling execute_file_proxy_method");
-                return self.execute_file_proxy_method(file_proxy, method, arguments);
-            } else {
-                eprintln!("❌ DEBUG: Object is NOT FileBoxProxy");
-            }
-        }
-        
         // ResultBox method calls
         if let Some(result_box) = obj_value.as_any().downcast_ref::<crate::box_trait::ResultBox>() {
             return self.execute_result_method(result_box, method, arguments);