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/fastadmin/mailbox.less

@@ -0,0 +1,88 @@
+/*
+ * Page: Mailbox
+ * -------------
+ */
+.mailbox-messages {
+  > .table {
+    margin: 0;
+  }
+}
+
+.mailbox-controls {
+  padding: 5px;
+  &.with-border {
+    border-bottom: 1px solid @box-border-color;
+  }
+}
+
+.mailbox-read-info {
+  border-bottom: 1px solid @box-border-color;
+  padding: 10px;
+  h3 {
+    font-size: 20px;
+    margin: 0;
+  }
+  h5 {
+    margin: 0;
+    padding: 5px 0 0 0;
+  }
+}
+
+.mailbox-read-time {
+  color: #999;
+  font-size: 13px;
+}
+
+.mailbox-read-message {
+  padding: 10px;
+}
+
+.mailbox-attachments {
+  &:extend(.list-unstyled);
+  li {
+    float: left;
+    width: 200px;
+    border: 1px solid #eee;
+    margin-bottom: 10px;
+    margin-right: 10px;
+  }
+}
+
+.mailbox-attachment-name {
+  font-weight: bold;
+  color: #666;
+}
+
+.mailbox-attachment-icon,
+.mailbox-attachment-info,
+.mailbox-attachment-size {
+  display: block;
+}
+
+.mailbox-attachment-info {
+  padding: 10px;
+  background: #f4f4f4;
+}
+
+.mailbox-attachment-size {
+  color: #999;
+  font-size: 12px;
+}
+
+.mailbox-attachment-icon {
+  text-align: center;
+  font-size: 65px;
+  color: #666;
+  padding: 20px 10px;
+  &.has-img {
+    padding: 0;
+    > img {
+      max-width: 100%;
+      height: auto;
+    }
+  }
+}
+
+.mailbox-attachment-close {
+  &:extend(.close);
+}