feat(Common): Restore Effect module for ActionEffect system

Re-add the `Effect` module to the public API in Library.rs. This module defines the core `ActionEffect` trait and associated types that power Common's abstract effect system used across Mountain, Cocoon, and other elements.

The module was previously removed during a deprecation pass but is needed as the foundational abstraction for the editor's effect-based architecture.

Author: NikolaRHristov

Source/Library.rs

@@ -55,6 +55,8 @@
 //!
 //! Full setup: <https://github.com/CodeEditorLand/Land>
 
+pub mod Effect;
+
 pub mod Environment;
 
 pub mod Error;