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-less/mixins/text-overflow.less

@@ -0,0 +1,8 @@
+// Text overflow
+// Requires inline-block or block for proper styling
+
+.text-overflow() {
+  overflow: hidden;
+  text-overflow: ellipsis;
+  white-space: nowrap;
+}