refactor(joinir): Phase 286 P3.2 cleanup + normalizer modularization

## Legacy Pattern5 削除 (488行)
- pattern5_infinite_early_exit.rs 完全削除
- LOOP_PATTERNS テーブルからエントリ削除
- Plan extractor が SSOT

## Normalizer 分割 (3294行 → 12ファイル)
- helpers.rs: 共通ヘルパー関数
- pattern*.rs: 各パターン専用ファイル
- mod.rs: ディスパッチャ

## ドキュメント更新
- Phase 286 README: クリーンアップ完了・Fail-Fast方針記載
- Phase 287 README: 将来計画

quick smoke 154/154 PASS

🤖 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/router.rs

@@ -358,18 +358,14 @@ pub(crate) struct LoopPatternEntry {
 ///
 /// **IMPORTANT**: Patterns are tried in array order (SSOT).
 /// Array order defines priority - earlier entries are tried first.
-/// Pattern5 (most specific) → Pattern4 → Pattern3 → Pattern1 → Pattern2
+/// Pattern4 → Pattern8 → Pattern9 → Pattern3 → Pattern1 → Pattern2
 ///
 /// # Current Patterns (Structure-based detection, established Phase 131-11+)
 ///
-/// Pattern detection strategies (updated Phase 282 P0):
+/// Pattern detection strategies (updated Phase 286):
 /// - Pattern6/7: ExtractionBased (Plan line, Phase 273+)
-/// - Pattern8/9: ExtractionBased (extraction functions, already implemented)
-/// - Pattern1-5: StructureBased (LoopFeatures classification, legacy)
-///
-/// - Pattern 5: Infinite Loop with Early Exit (llvm_stage3_loop_only.hako) [Phase 131-11]
-///   - Detection: pattern_kind == InfiniteEarlyExit
-///   - Structure: is_infinite_loop && has_break && has_continue
+/// - Pattern5/8/9: ExtractionBased (extraction functions, Plan line Phase 286+)
+/// - Pattern1-4: StructureBased (LoopFeatures classification, legacy)
 ///
 /// - Pattern 4: Loop with Continue (loop_continue_pattern4.hako)
 ///   - Detection: pattern_kind == Pattern4Continue
@@ -388,12 +384,8 @@ pub(crate) struct LoopPatternEntry {
 ///   - Structure: has_break && !has_continue
 ///
 /// Note: func_name is now only used for debug logging, not pattern detection
+/// Phase 286: Pattern5 removed (migrated to Plan-based routing)
 pub(crate) static LOOP_PATTERNS: &[LoopPatternEntry] = &[
-    LoopPatternEntry {
-        name: "Pattern5_InfiniteEarlyExit",
-        detect: super::pattern5_infinite_early_exit::can_lower,
-        lower: super::pattern5_infinite_early_exit::lower,
-    },
     LoopPatternEntry {
         name: "Pattern4_WithContinue",
         detect: super::pattern4_with_continue::can_lower,