refactor(joinir): Issue 1.4 - condition_to_joinir.rs modularization (74% modularization)

- condition_env.rs (182行): ConditionEnv + ConditionBinding
- condition_lowerer.rs (522行): Core AST → JoinIR lowering
- condition_var_extractor.rs (198行): Variable extraction from AST
- condition_to_joinir.rs (152行): Orchestrator (re-export API)

Before: 596行 (single file)
After: 1054行 (4 files, 152行 orchestrator)

Box Theory: Single responsibility separation
- Environment management isolated
- Lowering logic extracted
- Variable extraction separate
- Clean API orchestration

Build: ✅ Pass (0 errors)
Tests: ✅ All module tests included

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

src/mir/builder/control_flow/joinir/patterns/pattern2_with_break.rs

@@ -110,7 +110,7 @@ impl MirBuilder {
         }
 
         // Phase 171-fix Debug: Log condition bindings
-        eprintln!("[cf_loop/pattern2] Phase 171-fix: ConditionEnv contains {} variables:", env.name_to_join.len());
+        eprintln!("[cf_loop/pattern2] Phase 171-fix: ConditionEnv contains {} variables:", env.len());
         eprintln!("  Loop param '{}' → JoinIR ValueId(0)", loop_var_name);
         if !condition_bindings.is_empty() {
             eprintln!("  {} condition-only bindings:", condition_bindings.len());