feat: 后端全量更新 - 含所有本次需求

- Contract.php: 返回合约账户余额(balance_contract)
- My.php: 地址管理增加BTC/ETH
- AppContract.php: 一键平仓(closeall)
- AppProxy.php: 代理专属注册链接 + 分级权限(L1/L2)
- site.php: 手续费减半(0.018→0.009)
- agent_permission_setup.sql: 代理权限SQL
- crypto_news_crawler.py: 新闻自动采集脚本

public/assets/less/fastadmin/carousel.less

@@ -0,0 +1,18 @@
+/*
+ * Component: Carousel
+ * -------------------
+ */
+.carousel-control {
+  &.left,
+  &.right {
+    background-image: none;
+  }
+  > .fa {
+    font-size: 40px;
+    position: absolute;
+    top: 50%;
+    z-index: 5;
+    display: inline-block;
+    margin-top: -20px;
+  }
+}