refactor: Extract utilities from control_flow.rs (Phase 6)

- Created utils.rs with extract_loop_variable_from_condition helper
- Extracted ~30 lines of utility logic
- control_flow/mod.rs now delegates to utils module
- All builds pass, no behavior changes

src/mir/builder/control_flow/utils.rs

@@ -0,0 +1,53 @@
+//! Control flow utility functions.
+//!
+//! This module provides helper functions for control flow analysis and manipulation.
+
+use crate::ast::{ASTNode, BinaryOperator};
+
+/// Extract loop variable name from condition.
+///
+/// # Examples
+///
+/// - For `i < 3`, extracts `i`
+/// - For `arr.length() > 0`, extracts `arr`
+///
+/// # Implementation
+///
+/// This is a minimal implementation that handles simple comparison patterns.
+/// It looks for binary comparison operators (< > <= >=) and extracts the
+/// variable name from the left side of the comparison.
+///
+/// # Errors
+///
+/// Returns an error if:
+/// - The condition is not a binary comparison
+/// - The left side of the comparison is not a simple variable
+pub(in crate::mir::builder) fn extract_loop_variable_from_condition(
+    condition: &ASTNode,
+) -> Result<String, String> {
+    match condition {
+        ASTNode::BinaryOp {
+            operator, left, ..
+        } if matches!(
+            operator,
+            BinaryOperator::Less
+                | BinaryOperator::Greater
+                | BinaryOperator::LessEqual
+                | BinaryOperator::GreaterEqual
+        ) =>
+        {
+            // Binary comparison: extract variable from left side
+            match &**left {
+                ASTNode::Variable { name, .. } => Ok(name.clone()),
+                _ => Err(format!(
+                    "[cf_loop/pattern1] Cannot extract loop variable from condition: {:?}",
+                    condition
+                )),
+            }
+        }
+        _ => Err(format!(
+            "[cf_loop/pattern1] Unsupported loop condition pattern: {:?}",
+            condition
+        )),
+    }
+}