feat: add USDT warning for Aster exchange configuration

Added warning message to inform users that Aster only tracks USDT balance, preventing P&L calculation errors from asset price fluctuations.

Why this is important:
- Aster trader only tracks USDT balance (aster_trader.go:453)
- If users use BNB/ETH as margin, price fluctuations will cause:
  * Initial balance becomes inaccurate
  * P&L statistics will be wrong
  * Example: 10 BNB @ $100 = $1000, if BNB drops to $90, real equity is $900 but system still shows $1000

Changes:
- Added asterUsdtWarning translation in both EN and ZH
- Added red warning box below Aster private key field
- Clear message: "Please use USDT as margin currency"

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

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

web/src/components/AITradersPage.tsx

@@ -1899,6 +1899,26 @@ function ExchangeConfigModal({
                       required
                     />
                   </div>
+
+                  {/* USDT 警告提示 */}
+                  <div
+                    className="p-4 rounded"
+                    style={{
+                      background: 'rgba(246, 70, 93, 0.1)',
+                      border: '1px solid rgba(246, 70, 93, 0.3)',
+                    }}
+                  >
+                    <div
+                      className="text-sm font-semibold mb-2 flex items-center gap-2"
+                      style={{ color: '#F6465D' }}
+                    >
+                      <AlertTriangle className="w-4 h-4" />
+                      {t('securityWarning', language)}
+                    </div>
+                    <div className="text-xs" style={{ color: '#848E9C' }}>
+                      {t('asterUsdtWarning', language)}
+                    </div>
+                  </div>
                 </>
               )}
 

web/src/i18n/translations.ts

@@ -203,6 +203,8 @@ export const translations = {
       'API wallet address - Generate from Aster API Wallet page',
     asterPrivateKeyDesc:
       'API wallet private key - Only used locally for signing, never transmitted',
+    asterUsdtWarning:
+      'Important: Aster only tracks USDT balance. Please ensure you use USDT as margin currency to avoid P&L calculation errors caused by price fluctuations of other assets (BNB, ETH, etc.)',
     testnetDescription:
       'Enable to connect to exchange test environment for simulated trading',
     securityWarning: 'Security Warning',
@@ -670,6 +672,8 @@ export const translations = {
       'API 钱包地址 - 从 Aster API 钱包页面生成',
     asterPrivateKeyDesc:
       'API 钱包私钥 - 仅在本地用于签名，不会被传输',
+    asterUsdtWarning:
+      '重要提示：Aster 仅统计 USDT 余额。请确保您使用 USDT 作为保证金币种，避免其他资产（BNB、ETH等）的价格波动导致盈亏统计错误',
     testnetDescription: '启用后将连接到交易所测试环境,用于模拟交易',
     securityWarning: '安全提示',
     saveConfiguration: '保存配置',