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/mir/mod.rs

@@ -13,7 +13,6 @@ pub mod builder;
 pub mod verification;
 pub mod ownership_verifier_simple; // Simple ownership forest verification for current MIR
 pub mod printer;
-pub mod optimizer; // Phase 3: Effect System based optimization passes
 pub mod value_id;
 pub mod effect;
 
@@ -26,7 +25,6 @@ pub use builder::MirBuilder;
 pub use verification::{MirVerifier, VerificationError};
 pub use ownership_verifier_simple::{OwnershipVerifier, OwnershipError, OwnershipStats}; // Simple ownership forest verification
 pub use printer::MirPrinter;
-pub use optimizer::{MirOptimizer, OptimizationStats}; // Phase 3: Effect System optimizations
 pub use value_id::{ValueId, LocalId, ValueIdGenerator};
 pub use effect::{EffectMask, Effect};