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/boxes/future/mod.rs

@@ -3,7 +3,6 @@
 // 参考: 既存Boxの設計思想
 
 use crate::box_trait::{NyashBox, StringBox, BoolBox, BoxCore, BoxBase};
-use crate::bid::{BidBridge, BidHandle, BidType, BidError, BoxRegistry};
 use std::any::Any;
 use std::sync::RwLock;
 
@@ -147,25 +146,6 @@ impl std::fmt::Display for NyashFutureBox {
     }
 }
 
-impl BidBridge for NyashFutureBox {
-    fn to_bid_handle(&self, registry: &mut BoxRegistry) -> Result<BidHandle, BidError> {
-        use std::sync::Arc;
-        let arc_box: Arc<dyn NyashBox> = Arc::new(self.clone());
-        let handle = registry.register_box(
-            crate::bid::types::BoxTypeId::FutureBox as u32,
-            arc_box
-        );
-        Ok(handle)
-    }
-    
-    fn bid_type(&self) -> BidType {
-        BidType::Handle { 
-            type_id: crate::bid::types::BoxTypeId::FutureBox as u32,
-            instance_id: 0  // Will be filled by registry
-        }
-    }
-}
-
 // Export NyashFutureBox as FutureBox for consistency
 pub type FutureBox = NyashFutureBox;