feat(joinir): Phase 33-22 CommonPatternInitializer & JoinIRConversionPipeline integration

Unifies initialization and conversion logic across all 4 loop patterns,
eliminating code duplication and establishing single source of truth.

## Changes

### Infrastructure (New)
- CommonPatternInitializer (117 lines): Unified loop var extraction + CarrierInfo building
- JoinIRConversionPipeline (127 lines): Unified JoinIR→MIR→Merge flow

### Pattern Refactoring
- Pattern 1: Uses CommonPatternInitializer + JoinIRConversionPipeline (-25 lines)
- Pattern 2: Uses CommonPatternInitializer + JoinIRConversionPipeline (-25 lines)
- Pattern 3: Uses CommonPatternInitializer + JoinIRConversionPipeline (-25 lines)
- Pattern 4: Uses CommonPatternInitializer + JoinIRConversionPipeline (-40 lines)

### Code Reduction
- Total reduction: ~115 lines across all patterns
- Zero code duplication in initialization/conversion
- Pattern files: 806 lines total (down from ~920)

### Quality Improvements
- Single source of truth for initialization
- Consistent conversion flow across all patterns
- Guaranteed boundary.loop_var_name setting (prevents SSA-undef bugs)
- Improved maintainability and testability

### Testing
- All 4 patterns tested and passing:
  - Pattern 1 (Simple While): ✅
  - Pattern 2 (With Break): ✅
  - Pattern 3 (If-Else PHI): ✅
  - Pattern 4 (With Continue): ✅

### Documentation
- Phase 33-22 inventory and results document
- Updated joinir-architecture-overview.md with new infrastructure

## Breaking Changes
None - pure refactoring with no API changes

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

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

docs/development/current/main/00-Overview.md

@@ -14,3 +14,8 @@
 - 新規 MIR 命令の追加。
 - try/finally と continue/break の相互作用（次段）。
 
+## JoinIR / Selfhost 関連の入口
+
+- JoinIR 全体のアーキテクチャと箱の関係は  
+  `docs/development/current/main/joinir-architecture-overview.md` を参照してね。
+- selfhost / .hako 側から JoinIR を使うときも、この設計を SSOT として運用する方針だよ。