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

thinkphp/codecov.yml

@@ -0,0 +1,12 @@
+comment:
+  layout: header, changes, diff
+coverage:
+  ignore:
+  - base.php
+  - helper.php
+  - convention.php
+  - lang/zh-cn.php
+  - start.php
+  - console.php
+  status:
+    patch: false