feat(joinir): Phase 131-11 A-C - InfiniteEarlyExit パターン追加（検出部分）

## Step A: Feature Detection
- LoopPatternKind::InfiniteEarlyExit (Pattern 5) 追加
- LoopFeatures::is_infinite_loop フィールド追加
- detect_infinite_loop() で loop(true) 検出

## Step B: Classification Logic
- classify() を更新: Pattern 5 を Pattern 4 より優先
- Pattern 4 を狭化: has_continue && !has_break のみ
- 誤ルーティング完全除去

## Step C: Pattern Module
- pattern5_infinite_early_exit.rs 新規作成
- Fail-Fast 設計: 超狭い shape guard
- lowering はスケルトン（Phase 131-11-D で実装）

## 動作確認
- Pattern 5 正常検出 ✅
- Shape guards 動作（1 break, 1 continue, 1 carrier）✅
- Pattern 4 誤ルーティング回避 ✅

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

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

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

@@ -55,6 +55,7 @@ pub(in crate::mir::builder) mod pattern2_with_break;
 pub(in crate::mir::builder) mod pattern3_with_if_phi;
 pub(in crate::mir::builder) mod pattern4_carrier_analyzer;
 pub(in crate::mir::builder) mod pattern4_with_continue;
+pub(in crate::mir::builder) mod pattern5_infinite_early_exit; // Phase 131-11
 pub(in crate::mir::builder) mod pattern_pipeline;
 pub(in crate::mir::builder) mod router;
 pub(in crate::mir::builder) mod trim_loop_lowering; // Phase 180: Dedicated Trim/P5 lowering module