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/font-awesome/scss/font-awesome.scss

@@ -0,0 +1,18 @@
+/*!
+ *  Font Awesome 4.7.0 by @davegandy - http://fontawesome.io - @fontawesome
+ *  License - http://fontawesome.io/license (Font: SIL OFL 1.1, CSS: MIT License)
+ */
+
+@import "variables";
+@import "mixins";
+@import "path";
+@import "core";
+@import "larger";
+@import "fixed-width";
+@import "list";
+@import "bordered-pulled";
+@import "animated";
+@import "rotated-flipped";
+@import "stacked";
+@import "icons";
+@import "screen-reader";