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/join_ir/lowering/mod.rs

@@ -22,7 +22,10 @@
 pub mod bool_expr_lowerer; // Phase 168: Boolean expression lowering for complex conditions
 pub mod carrier_info; // Phase 196: Carrier metadata for loop lowering
 pub mod common;
-pub mod condition_to_joinir; // Phase 169: JoinIR condition lowering helper
+pub mod condition_env; // Phase 171-fix: Condition expression environment
+pub mod condition_lowerer; // Phase 171-fix: Core condition lowering logic
+pub mod condition_to_joinir; // Phase 169: JoinIR condition lowering orchestrator (refactored)
+pub mod condition_var_extractor; // Phase 171-fix: Variable extraction from condition AST
 pub mod continue_branch_normalizer; // Phase 33-19: Continue branch normalization for Pattern B
 pub mod loop_update_analyzer; // Phase 197: Update expression analyzer for carrier semantics
 pub mod loop_update_summary; // Phase 170-C-2: Update pattern summary for shape detection