feat: 订单列表支持分页查询，分页大小可选 20/50/100

- /api/orders/my 新增 page/page_size 参数，返回分页信息和全局状态统计
- 用户订单页：分页控件（首/上/下/末页）+ 分页大小选择，摘要卡片改为全局统计
- 管理员订单页：分页大小选择器（20/50/100）+ 首尾页跳转按钮

src/app/admin/page.tsx

@@ -43,6 +43,7 @@ function AdminContent() {
   const [orders, setOrders] = useState<AdminOrder[]>([]);
   const [total, setTotal] = useState(0);
   const [page, setPage] = useState(1);
+  const [pageSize, setPageSize] = useState(20);
   const [totalPages, setTotalPages] = useState(1);
   const [statusFilter, setStatusFilter] = useState('');
   const [loading, setLoading] = useState(true);
@@ -54,7 +55,7 @@ function AdminContent() {
     if (!token) return;
     setLoading(true);
     try {
-      const params = new URLSearchParams({ token, page: String(page), page_size: '20' });
+      const params = new URLSearchParams({ token, page: String(page), page_size: String(pageSize) });
       if (statusFilter) params.set('status', statusFilter);
 
       const res = await fetch(`/api/admin/orders?${params}`);
@@ -75,7 +76,7 @@ function AdminContent() {
     } finally {
       setLoading(false);
     }
-  }, [token, page, statusFilter]);
+  }, [token, page, pageSize, statusFilter]);
 
   useEffect(() => {
     fetchOrders();
@@ -198,14 +199,36 @@ function AdminContent() {
       </div>
 
       {/* Pagination */}
-      {totalPages > 1 && (
-        <div className="mt-4 flex items-center justify-between text-sm text-gray-500">
-          <span>共 {total} 条记录</span>
-          <div className="flex gap-2">
+      <div className="mt-4 flex flex-wrap items-center justify-between gap-3 text-sm text-gray-500">
+        <div className="flex items-center gap-2">
+          <span>共 {total} 条，每页</span>
+          {[20, 50, 100].map((s) => (
+            <button
+              key={s}
+              onClick={() => { setPageSize(s); setPage(1); }}
+              className={`rounded border px-2.5 py-1 text-xs font-medium transition-colors ${
+                pageSize === s
+                  ? 'border-blue-500 bg-blue-50 text-blue-700'
+                  : 'border-gray-300 text-gray-600 hover:bg-gray-100'
+              }`}
+            >
+              {s}
+            </button>
+          ))}
+        </div>
+        {totalPages > 1 && (
+          <div className="flex items-center gap-1.5">
+            <button
+              onClick={() => setPage(1)}
+              disabled={page <= 1}
+              className="rounded border px-2.5 py-1 disabled:opacity-40 hover:bg-gray-100"
+            >
+              ««
+            </button>
             <button
               onClick={() => setPage((p) => Math.max(1, p - 1))}
               disabled={page <= 1}
-              className="rounded border px-3 py-1 disabled:opacity-50"
+              className="rounded border px-3 py-1 disabled:opacity-40 hover:bg-gray-100"
             >
               上一页
             </button>
@@ -215,13 +238,20 @@ function AdminContent() {
             <button
               onClick={() => setPage((p) => Math.min(totalPages, p + 1))}
               disabled={page >= totalPages}
-              className="rounded border px-3 py-1 disabled:opacity-50"
+              className="rounded border px-3 py-1 disabled:opacity-40 hover:bg-gray-100"
             >
               下一页
             </button>
+            <button
+              onClick={() => setPage(totalPages)}
+              disabled={page >= totalPages}
+              className="rounded border px-2.5 py-1 disabled:opacity-40 hover:bg-gray-100"
+            >
+              »»
+            </button>
           </div>
-        </div>
-      )}
+        )}
+      </div>
 
       {/* Order Detail */}
       {detailOrder && <OrderDetail order={detailOrder} onClose={() => setDetailOrder(null)} />}