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/bootstrap/mixins/list-group.less

@@ -0,0 +1,30 @@
+// List Groups
+
+.list-group-item-variant(@state; @background; @color) {
+  .list-group-item-@{state} {
+    color: @color;
+    background-color: @background;
+
+    a&,
+    button& {
+      color: @color;
+
+      .list-group-item-heading {
+        color: inherit;
+      }
+
+      &:hover,
+      &:focus {
+        color: @color;
+        background-color: darken(@background, 5%);
+      }
+      &.active,
+      &.active:hover,
+      &.active:focus {
+        color: #fff;
+        background-color: @color;
+        border-color: @color;
+      }
+    }
+  }
+}