docs: README + site 更新 v0.1.13 新特性（事务回滚/子查询/外键级联/连接池）

site/demo.html

@@ -82,7 +82,7 @@
     <a href="docs.html">文档</a>
     <a href="demo.html" class="nav-active">演示</a>
   </nav>
-  <div class="status"><span class="dot"></span> Memory 模式 — v0.1.12</div>
+  <div class="status"><span class="dot"></span> Memory 模式 — v0.1.13</div>
 </header>
 
 <div class="main">
@@ -112,6 +112,7 @@ SELECT COUNT(*) as total_users, AVG(age) as avg_age FROM users;</textarea>
         <button class="btn btn-preset" onclick="loadPreset('agg')">📊 聚合</button>
         <button class="btn btn-preset" onclick="loadPreset('ddl')">🏗 DDL</button>
         <button class="btn btn-preset" onclick="loadPreset('crud')">✏️ CRUD</button>
+        <button class="btn btn-preset" onclick="loadPreset('subquery')">🔍 子查询</button>
       </div>
     </div>
   </div>
@@ -370,7 +371,21 @@ SELECT * FROM users WHERE id = '9';
 DELETE FROM users WHERE id = '9';
 
 -- 确认
-SELECT COUNT(*) as user_count FROM users;`
+SELECT COUNT(*) as user_count FROM users;`,
+  subquery: `-- IN 子查询：有订单的用户
+SELECT name, email FROM users
+WHERE id IN (SELECT user_id FROM orders);
+
+-- NOT IN 子查询：没有订单的用户
+SELECT name, email FROM users
+WHERE id NOT IN (SELECT user_id FROM orders);
+
+-- 标量子查询：消费最高的用户
+SELECT name, age FROM users
+WHERE id IN (
+  SELECT user_id FROM orders
+  WHERE amount = (SELECT MAX(amount) FROM orders)
+);`
 };
 
 function loadPreset(name) {