refactor(joinir): Phase 244 - ConditionLoweringBox trait unification

Unify condition lowering logic across Pattern 2/4 with trait-based API.

New infrastructure:
- condition_lowering_box.rs: ConditionLoweringBox trait + ConditionContext (293 lines)
- ExprLowerer implements ConditionLoweringBox trait (+51 lines)

Pattern migrations:
- Pattern 2 (loop_with_break_minimal.rs): Use trait API
- Pattern 4 (loop_with_continue_minimal.rs): Use trait API

Benefits:
- Unified condition lowering interface
- Extensible for future lowering strategies
- Clean API boundary between patterns and lowering logic
- Zero code duplication

Test results: 911/911 PASS (+2 new tests)

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

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

docs/development/current/main/phase218-jsonparser-if-sum-min.md

@@ -256,3 +256,5 @@ Phantom `count` carrier detected based on name alone.
 **Next**: Fix carrier detection (Phase 219), then retry JsonParser pattern
 
 **The investigation was successful - we found why AST-based lowerer doesn't activate!** 🔍
+Status: Active  
+Scope: JsonParser if-sum min ケース（JoinIR v2）