feat(joinir): Phase 240-EX - Pattern2 header condition ExprLowerer integration

Implementation:
- Add make_pattern2_scope_manager() helper for DRY
- Header conditions use ExprLowerer for supported patterns
- Legacy fallback for unsupported patterns
- Fail-Fast on supported patterns that fail

Tests:
- 4 new tests (all pass)
- test_expr_lowerer_supports_simple_header_condition_i_less_literal
- test_expr_lowerer_supports_header_condition_var_less_var
- test_expr_lowerer_header_condition_generates_expected_instructions
- test_pattern2_header_condition_via_exprlowerer

Also: Archive old phase documentation (34k lines removed)

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

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

docs/development/current/main/phase33-17-joinir-modularization-analysis.md

@@ -1,3 +1,6 @@
+Status: Active  
+Scope: Phase 33-17 の JoinIR モジュール化分析の要約（現行参照用）。詳細メモは archive 側へ移行。
+
 # Phase 33-17: JoinIR モジュール化分析
 
 ## 実行日: 2025-12-07