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/bootstrap/less/responsive-embed.less

@@ -0,0 +1,35 @@
+// Embeds responsive
+//
+// Credit: Nicolas Gallagher and SUIT CSS.
+
+.embed-responsive {
+  position: relative;
+  display: block;
+  height: 0;
+  padding: 0;
+  overflow: hidden;
+
+  .embed-responsive-item,
+  iframe,
+  embed,
+  object,
+  video {
+    position: absolute;
+    top: 0;
+    bottom: 0;
+    left: 0;
+    width: 100%;
+    height: 100%;
+    border: 0;
+  }
+}
+
+// Modifier class for 16:9 aspect ratio
+.embed-responsive-16by9 {
+  padding-bottom: 56.25%;
+}
+
+// Modifier class for 4:3 aspect ratio
+.embed-responsive-4by3 {
+  padding-bottom: 75%;
+}