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/border-radius.less

@@ -0,0 +1,21 @@
+// Single side border-radius
+
+.border-top-radius(@radius) {
+  border-top-right-radius: @radius;
+  border-top-left-radius: @radius;
+}
+
+.border-right-radius(@radius) {
+  border-bottom-right-radius: @radius;
+  border-top-right-radius: @radius;
+}
+
+.border-bottom-radius(@radius) {
+  border-bottom-right-radius: @radius;
+  border-bottom-left-radius: @radius;
+}
+
+.border-left-radius(@radius) {
+  border-bottom-left-radius: @radius;
+  border-top-left-radius: @radius;
+}