fix(ui): 充值页面隐藏 BSC 和 DST 网络选项

- 注释掉 BSC 和 DST 网络按钮，只保留 KAVA
- 代码保留在程序中，便于后续恢复

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

frontend/mobile-app/lib/features/deposit/presentation/pages/deposit_usdt_page.dart

@@ -294,22 +294,22 @@ class _DepositUsdtPageState extends ConsumerState<DepositUsdtPage> {
                 isSelected: _selectedNetwork == NetworkType.kava,
               ),
             ),
-            // BSC 网络按钮
-            Expanded(
-              child: _buildNetworkButton(
-                label: 'BSC',
-                network: NetworkType.bsc,
-                isSelected: _selectedNetwork == NetworkType.bsc,
-              ),
-            ),
-            // DST 网络按钮
-            Expanded(
-              child: _buildNetworkButton(
-                label: 'DST',
-                network: NetworkType.dst,
-                isSelected: _selectedNetwork == NetworkType.dst,
-              ),
-            ),
+            // BSC 网络按钮（暂时隐藏）
+            // Expanded(
+            //   child: _buildNetworkButton(
+            //     label: 'BSC',
+            //     network: NetworkType.bsc,
+            //     isSelected: _selectedNetwork == NetworkType.bsc,
+            //   ),
+            // ),
+            // DST 网络按钮（暂时隐藏）
+            // Expanded(
+            //   child: _buildNetworkButton(
+            //     label: 'DST',
+            //     network: NetworkType.dst,
+            //     isSelected: _selectedNetwork == NetworkType.dst,
+            //   ),
+            // ),
           ],
         ),
       ),