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/mod.rs

@@ -6,6 +6,7 @@
 //! - Phase 3: JoinIR routing (joinir/routing.rs) ✅
 //! - Phase 4: Merge implementation (joinir/merge/) ✅
 //! - Phase 5: Exception handling (exception/) ✅
+//! - Phase 6: Utility functions (utils.rs) ✅
 
 use super::ValueId;
 use crate::ast::ASTNode;
@@ -19,6 +20,9 @@ pub(in crate::mir::builder) mod joinir;
 // Phase 5: Exception handling
 pub(in crate::mir::builder) mod exception;
 
+// Phase 6: Utility functions
+pub(in crate::mir::builder) mod utils;
+
 impl super::MirBuilder {
     /// Control-flow: block
     pub(super) fn cf_block(&mut self, statements: Vec<ASTNode>) -> Result<ValueId, String> {
@@ -138,35 +142,9 @@ impl super::MirBuilder {
     /// For `i < 3`, extracts `i`.
     /// For `arr.length() > 0`, extracts `arr`.
     ///
-    /// This is a minimal implementation that handles simple comparison patterns.
+    /// Delegates to utils::extract_loop_variable_from_condition for implementation.
     fn extract_loop_variable_from_condition(&self, condition: &ASTNode) -> Result<String, String> {
-        use crate::ast::BinaryOperator;
-
-        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
-            )),
-        }
+        utils::extract_loop_variable_from_condition(condition)
     }
 
     /// Control-flow: throw