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

src/mir/builder/builder_calls.rs

@@ -839,8 +839,8 @@ impl super::MirBuilder {
                 self.variable_map.insert(p.clone(), pid);
             }
         }
-        let program_ast = function_lowering::wrap_in_program(body);
-        let _last = self.build_expression(program_ast)?;
+        // Lower statements in sequence to preserve def→use order
+        let _last = self.cf_block(body)?;
         if !returns_value && !self.is_current_block_terminated() {
             let void_val = crate::mir::builder::emission::constant::emit_void(self);
             self.emit_instruction(MirInstruction::Return {