fix(mir): PHI検証panic修正 - update_cfg()を検証前に呼び出し

A案実装: debug_verify_phi_inputs呼び出し前にCFG predecessorを更新

修正箇所（7箇所）:
- src/mir/builder/phi.rs:50, 73, 132, 143
- src/mir/builder/ops.rs:273, 328, 351

根本原因:
- Branch/Jump命令でsuccessorは即座に更新
- predecessorはupdate_cfg()で遅延再構築
- PHI検証が先に実行されてpredecessor未更新でpanic

解決策:
- 各debug_verify_phi_inputs呼び出し前に
  if let Some(func) = self.current_function.as_mut() {
      func.update_cfg();
  }
  を挿入してCFGを同期

影響: if/else文、論理演算子(&&/||)のPHI生成が正常動作

lang/src/vm/collect_empty_args_using_smoke.hako

@@ -5,9 +5,9 @@ static box Main {
     local json = "{\"kind\":\"Program\",\"statements\":[{\"kind\":\"Print\",\"expression\":{\"kind\":\"FunctionCall\",\"name\":\"echo\",\"arguments\":[]}},{\"kind\":\"Print\",\"expression\":{\"kind\":\"FunctionCall\",\"name\":\"itoa\",\"arguments\":[]}}]}"
 
     local arr = new MiniVm().collect_prints(json)
-    print("DEBUG: arr.size=" + arr.size())
+    print("DEBUG: arr.size=" + arr.length())
     local i = 0
-    loop (i < arr.size()) { print(arr.get(i))  i = i + 1 }
+    loop (i < arr.length()) { print(arr.get(i))  i = i + 1 }
     return 0
   }
 }