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/docs.html

@@ -85,7 +85,10 @@
     <a href="#groupby">GROUP BY & 聚合</a>
     <a href="#where-ops">WHERE 操作符</a>
     <h4>高级特性</h4>
-    <a href="#transaction">事务</a>
+    <a href="#transaction">事务 & 回滚</a>
+    <a href="#subquery">子查询</a>
+    <a href="#foreign-key">外键级联</a>
+    <a href="#connection-pool">连接池</a>
     <a href="#migration">数据迁移</a>
     <a href="#export">导入导出</a>
     <a href="#plugin">插件 & 钩子</a>
@@ -189,6 +192,8 @@ db.<span class="f">isReady</span>();  <span class="c">// true</span>
   <tr><td><code>maxLength</code></td><td><code>number</code></td><td>字符串最大长度</td></tr>
   <tr><td><code>min</code>/<code>max</code></td><td><code>number</code></td><td>数值范围</td></tr>
   <tr><td><code>references</code></td><td><code>string</code></td><td>外键引用 <code>'table.column'</code></td></tr>
+  <tr><td><code>onDelete</code></td><td><code>'CASCADE'\|'SET NULL'\|'RESTRICT'</code></td><td>删除级联 🆕</td></tr>
+  <tr><td><code>onUpdate</code></td><td><code>'CASCADE'\|'SET NULL'\|'RESTRICT'</code></td><td>更新级联 🆕</td></tr>
 </table>
 
 <h2 id="sql-query">🔍 SQL 查询</h2>
@@ -352,21 +357,83 @@ db.<span class="f">isReady</span>();  <span class="c">// true</span>
   <span class="s">name</span>: { <span class="s">$like</span>: <span class="s">'A%'</span>, <span class="s">$ne</span>: <span class="s">'Admin'</span> },
 })</pre>
 
-<h2 id="transaction">🔒 事务</h2>
-<p>保证原子性，事务内步骤失败自动报错。</p>
+<h2 id="transaction">🔒 事务 & 回滚</h2>
+<p>v0.1.13 起支持真正的自动回滚：事务内任何一步失败，所有变更自动撤销。</p>
 
 <pre><span class="k">await</span> db.<span class="f">transaction</span>(<span class="k">async</span> (trx) => {
   <span class="c">// trx.table() 获取事务内表操作对象</span>
   <span class="k">await</span> trx.<span class="f">table</span>(<span class="s">'users'</span>).<span class="f">insert</span>({ <span class="s">id</span>: <span class="s">'3'</span>, <span class="s">name</span>: <span class="s">'Charlie'</span> });
   <span class="k">await</span> trx.<span class="f">table</span>(<span class="s">'orders'</span>).<span class="f">insert</span>({ <span class="s">id</span>: <span class="s">'o1'</span>, <span class="s">userId</span>: <span class="s">'3'</span>, <span class="s">amount</span>: <span class="n">99</span> });
-  <span class="k">await</span> trx.<span class="f">table</span>(<span class="s">'accounts'</span>).<span class="f">update</span>({ <span class="s">balance</span>: <span class="n">1</span> })
-    .<span class="f">where</span>({ <span class="s">userId</span>: <span class="s">'3'</span> })
-    .<span class="f">execute</span>();
-
-  <span class="c">// 也可返回结果</span>
-  <span class="k">return</span> <span class="s">'success'</span>;
+  <span class="c">// ✅ 全部成功 → 自动 commit</span>
+  <span class="c">// ❌ 任何一步失败 → 自动 rollback，数据恢复原状</span>
+  <span class="c">// Memory 引擎：快照回滚 | IndexedDB 引擎：延迟写入</span>
 });</pre>
 
+<h2 id="subquery">🔍 子查询</h2>
+<p>v0.1.13 新增子查询支持，可在 WHERE 条件中嵌套 SELECT。</p>
+
+<pre><span class="c">// IN 子查询 — 查询有高额订单的用户</span>
+<span class="k">await</span> db.<span class="f">query</span>(<span class="s">`SELECT * FROM users
+  WHERE id IN (SELECT user_id FROM orders WHERE amount > 100)`</span>);
+
+<span class="c">// 标量子查询 — 查询年龄等于平均年龄的用户</span>
+<span class="k">await</span> db.<span class="f">query</span>(<span class="s">`SELECT * FROM users
+  WHERE age = (SELECT AVG(age) FROM users)`</span>);
+
+<span class="c">// NOT IN 子查询</span>
+<span class="k">await</span> db.<span class="f">query</span>(<span class="s">`SELECT * FROM users
+  WHERE id NOT IN (SELECT user_id FROM orders)`</span>);</pre>
+
+<h2 id="foreign-key">🔗 外键级联</h2>
+<p>v0.1.13 支持外键级联操作，定义表时可指定 ON DELETE / ON UPDATE 行为。</p>
+
+<pre><span class="c">// 定义时指定外键 + 级联策略</span>
+<span class="k">await</span> db.<span class="f">defineTable</span>(<span class="s">'orders'</span>, {
+  <span class="s">id</span>: { <span class="s">type</span>: <span class="s">'string'</span>, <span class="s">primaryKey</span>: <span class="k">true</span> },
+  <span class="s">user_id</span>: {
+    <span class="s">type</span>: <span class="s">'string'</span>,
+    <span class="s">references</span>: <span class="s">'users.id'</span>,
+    <span class="s">onDelete</span>: <span class="s">'CASCADE'</span>,  <span class="c">// 删除用户时级联删除订单</span>
+    <span class="s">onUpdate</span>: <span class="s">'RESTRICT'</span>, <span class="c">// 禁止更新被引用的用户 ID</span>
+  },
+  <span class="s">amount</span>: { <span class="s">type</span>: <span class="s">'number'</span> },
+});
+
+<span class="c">// SQL DDL 同样支持</span>
+<span class="k">await</span> db.<span class="f">query</span>(<span class="s">`CREATE TABLE orders (
+  id STRING PRIMARY KEY,
+  user_id STRING REFERENCES users(id) ON DELETE CASCADE ON UPDATE RESTRICT,
+  amount NUMBER
+)`</span>);
+
+<span class="c">// 删除用户 → 其所有订单自动删除</span>
+<span class="k">await</span> db.<span class="f">query</span>(<span class="s">"DELETE FROM users WHERE id = '1'"</span>);</pre>
+
+<table>
+  <tr><th>级联选项</th><th>行为</th></tr>
+  <tr><td><code>CASCADE</code></td><td>级联删除/更新子表中的匹配行</td></tr>
+  <tr><td><code>SET NULL</code></td><td>将子表中的外键列设为 NULL</td></tr>
+  <tr><td><code>RESTRICT</code></td><td>禁止操作（默认行为）</td></tr>
+</table>
+
+<h2 id="connection-pool">🏊 连接池</h2>
+<p>v0.1.13 新增连接池管理器，避免重复创建同名数据库实例。</p>
+
+<pre><span class="c">// connect() — 获取或创建实例（单例复用）</span>
+<span class="k">const</span> db1 = <span class="k">await</span> <span class="f">MetonaSqlark.connect</span>({ <span class="s">name</span>: <span class="s">'my-app'</span>, <span class="s">mode</span>: <span class="s">'hybrid'</span> });
+<span class="k">const</span> db2 = <span class="k">await</span> <span class="f">MetonaSqlark.connect</span>({ <span class="s">name</span>: <span class="s">'my-app'</span> });
+<span class="c">// db1 === db2 — 复用已有实例，避免重复 open IndexedDB</span>
+
+<span class="c">// disconnect() — 释放连接（引用计数 -1）</span>
+<span class="k">await</span> db2.<span class="f">disconnect</span>(); <span class="c">// 引用计数: 2 → 1</span>
+<span class="k">await</span> db1.<span class="f">disconnect</span>(); <span class="c">// 引用计数: 1 → 0，自动 close()</span>
+
+<span class="c">// disconnectAll() — 强制关闭所有连接</span>
+<span class="k">await</span> <span class="f">MetonaSqlark.disconnectAll</span>();
+
+<span class="c">// getActiveConnections() — 查看活跃连接</span>
+<span class="f">MetonaSqlark.getActiveConnections</span>(); <span class="c">// ['my-app']</span></pre>
+
 <h2 id="migration">🔄 数据迁移</h2>
 <p>按版本号管理表结构变更。</p>