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/libs/eonasdan-bootstrap-datetimepicker/src/less/bootstrap-datetimepicker-build.less

@@ -0,0 +1,17 @@
+// Import bootstrap variables including default color palette and fonts
+@import "bootstrap/less/variables.less";
+
+// Import datepicker component
+@import "_bootstrap-datetimepicker.less";
+
+//this is here so the compiler doesn't complain about a missing bootstrap mixin
+.sr-only {
+  position: absolute;
+  width: 1px;
+  height: 1px;
+  margin: -1px;
+  padding: 0;
+  overflow: hidden;
+  clip: rect(0,0,0,0);
+  border: 0;
+}