fix(mir): Phase 131-9 - PHI 型推論修正（String→Integer）

Phase 131-9: MIR PHI 型推論バグ修正

問題:
- PHI が String 型として推論される
- 結果: 0,01,011（文字列連結）
- 期待: 0,1,2（整数 increment）

根本原因:
- PHI emission 時に circular dependency
- latch incoming value が PHI 型を継承
- 使用側（print）の型要求で String に

修正:
- src/mir/builder/lifecycle.rs (+75 lines):
  - Global PHI Type Inference Pass 追加
  - PHI 型を incoming values から再推論
  - PhiTypeResolver を再利用

MIR 変化:
- Before: %3: String = phi [%2, bb0], [%12, bb7]
- After:  %3: Integer = phi [%2, bb0], [%12, bb7]

テスト結果:
- Rust VM: 0,01,011 → 0,1,2 ✅ 完璧！
- LLVM: Segfault（別バグ、Phase 131-10 で対応）

箱化モジュール化:
- ✅ PhiTypeResolver 再利用
- ✅ 単一責任: PHI 型補正のみ
- ✅ Debug flag: NYASH_PHI_GLOBAL_DEBUG=1

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

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

src/mir/builder/lifecycle.rs

@@ -307,13 +307,88 @@ impl super::MirBuilder {
 
         let mut module = self.current_module.take().unwrap();
         let mut function = self.current_function.take().unwrap();
-        function.metadata.value_types = self.value_types.clone();
         // Phase 84-2: Copy命令型伝播（return型推論の前に実行）
         //
         // Loop exit や If merge の edge copy で発生する型欠如を解消する。
         // Copy チェーン: v1 → v2 → v3 で v1 の型が既知なら v2, v3 にも伝播。
         CopyTypePropagator::propagate(&function, &mut self.value_types);
 
+        // Phase 131-9: Global PHI type inference
+        //
+        // Infer types for ALL PHI nodes, not just return values.
+        // This fixes loop carrier PHIs that don't get inferred otherwise.
+        // Uses PhiTypeResolver to infer from incoming values (not usage).
+        //
+        // Bug: loop_min_while.hako PHI %3 was typed as String instead of Integer
+        // Cause: PHI incoming values unavailable at emission time
+        // Fix: Run PhiTypeResolver after CopyTypePropagator, before return type inference
+        //
+        // Collect ALL PHI dsts for re-inference (not just untyped)
+        // This is necessary because propagate_phi_meta may have assigned incorrect types
+        // due to circular dependencies (e.g., loop carrier PHIs)
+        let mut all_phi_dsts: Vec<ValueId> = Vec::new();
+        for (_bid, bb) in function.blocks.iter() {
+            for inst in &bb.instructions {
+                if let MirInstruction::Phi { dst, .. } = inst {
+                    if std::env::var("NYASH_PHI_GLOBAL_DEBUG").is_ok() {
+                        let existing_type = self.value_types.get(dst);
+                        eprintln!(
+                            "[lifecycle/phi-scan] {} PHI {:?} existing type: {:?}",
+                            function.signature.name, dst, existing_type
+                        );
+                    }
+                    all_phi_dsts.push(*dst);
+                }
+            }
+        }
+
+        if std::env::var("NYASH_PHI_GLOBAL_DEBUG").is_ok() {
+            eprintln!(
+                "[lifecycle/phi-scan] {} found {} total PHIs to re-infer",
+                function.signature.name,
+                all_phi_dsts.len()
+            );
+        }
+
+        // Re-infer types for ALL PHI nodes using PhiTypeResolver
+        // This fixes incorrect types assigned by propagate_phi_meta during circular dependencies
+        if !all_phi_dsts.is_empty() {
+            let phi_resolver = PhiTypeResolver::new(&function, &self.value_types);
+            let mut inferred_types: Vec<(ValueId, MirType)> = Vec::new();
+            for dst in all_phi_dsts {
+                if let Some(mt) = phi_resolver.resolve(dst) {
+                    // Check if type changed
+                    let existing_type = self.value_types.get(&dst);
+                    if existing_type.is_none() || existing_type != Some(&mt) {
+                        inferred_types.push((dst, mt));
+                    }
+                }
+            }
+
+            // Now insert/update all inferred types
+            for (dst, mt) in inferred_types {
+                let old_type = self.value_types.get(&dst).cloned();
+                self.value_types.insert(dst, mt.clone());
+                if std::env::var("NYASH_PHI_GLOBAL_DEBUG").is_ok() {
+                    if let Some(old) = old_type {
+                        eprintln!(
+                            "[lifecycle/phi-global] {} PHI {:?} type corrected: {:?} -> {:?}",
+                            function.signature.name, dst, old, mt
+                        );
+                    } else {
+                        eprintln!(
+                            "[lifecycle/phi-global] {} PHI {:?} type inferred: {:?}",
+                            function.signature.name, dst, mt
+                        );
+                    }
+                }
+            }
+        }
+
+        // Phase 131-9: Update function metadata with corrected types
+        // MUST happen after PHI type correction above
+        function.metadata.value_types = self.value_types.clone();
+
         // Phase 82-5: lifecycle.rs バグ修正 - terminator の Return のみをチェック
         //   問題: instructions を先に走査すると、中間値（const void 等）を誤って推論対象にしてしまう
         //   解決: terminator の Return のみをチェックし、実際の戻り値を正しく推論する