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/mod.rs

@@ -7,9 +7,7 @@
 
 // Import all necessary dependencies
 use crate::ast::{ASTNode, CatchClause};
-use crate::box_trait::{NyashBox, StringBox, IntegerBox, BoolBox, VoidBox, ArrayBox, ResultBox, ErrorBox, BoxCore};
-#[cfg(not(feature = "dynamic-file"))]
-use crate::box_trait::FileBox;
+use crate::box_trait::{NyashBox, StringBox, IntegerBox, BoolBox, VoidBox, ArrayBox, FileBox, ResultBox, ErrorBox, BoxCore};
 use crate::boxes::FutureBox;
 use crate::instance::InstanceBox;
 use crate::channel_box::ChannelBox;
@@ -42,16 +40,10 @@ mod math_methods;
 mod system_methods;
 mod web_methods;
 mod special_methods;
-#[cfg(feature = "dynamic-file")]
-mod plugin_loader;
 
 // Main interpreter implementation - will be moved from interpreter.rs
 pub use core::NyashInterpreter;
 
-// Dynamic plugin support
-#[cfg(feature = "dynamic-file")]
-pub use plugin_loader::{PluginLoader, FileBoxProxy};
-
 
 /// 実行制御フロー
 #[derive(Debug)]