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

addons/example/info.ini

@@ -0,0 +1,10 @@
+name = example
+title = 开发示例
+intro = FastAdmin多个开发示例
+author = FastAdmin
+website = https://www.fastadmin.net
+version = 1.1.1
+state = 1
+url = /addons/example
+license = regular
+licenseto = 16556