refactor(interpreter): Step 1 - Setup expressions module structure

- Move expressions.rs to expressions/mod.rs
- Create empty module files: operators.rs, calls.rs, access.rs, builtins.rs
- Add module declarations to mod.rs
- Build passes successfully

Next: Step 2 - Extract operator functions

src/interpreter/expressions/access.rs

@@ -0,0 +1,5 @@
+/*!
+ * Field access operations
+ */
+
+use super::*;

src/interpreter/expressions/builtins.rs

@@ -0,0 +1,5 @@
+/*!
+ * Builtin box methods and birth methods
+ */
+
+use super::*;

src/interpreter/expressions/calls.rs

@@ -0,0 +1,5 @@
+/*!
+ * Method calls and from delegation calls
+ */
+
+use super::*;

src/interpreter/expressions/mod.rs

@@ -6,6 +6,12 @@
  * Core philosophy: "Everything is Box" with clean expression evaluation
  */
 
+// Module declarations
+mod operators;
+mod calls;
+mod access;
+mod builtins;
+
 use super::*;
 use crate::ast::UnaryOperator;
 use crate::boxes::{buffer::BufferBox, JSONBox, HttpClientBox, StreamBox, RegexBox, IntentBox, SocketBox, HTTPServerBox, HTTPRequestBox, HTTPResponseBox};

src/interpreter/expressions/operators.rs

@@ -0,0 +1,5 @@
+/*!
+ * Binary and unary operator evaluation
+ */
+
+use super::*;