Route manual USDT/USDC convert through trading account (not funding).

Co-authored-by: Cursor <cursoragent@cursor.com>

frontend/src/pages/Settings.tsx

@@ -1474,8 +1474,8 @@ export default function SettingsPage() {
             onToggle={() => setFundsRulesOpen((v) => !v)}
           >
             <p>
-              币种兑换：对齐 OKX 现货市价 USDC-USDT，手动兑换在<strong>资金账户</strong>
-              内完成。参考价{" "}
+              币种兑换：对齐 OKX 现货市价 USDC-USDT，在<strong>交易账户</strong>
+              内完成（不走资金账户）。参考价{" "}
               {usdcRate != null ? `1 USDC ≈ ${usdcRate.toFixed(4)} USDT` : "—"}。
             </p>
             <p>
@@ -1489,7 +1489,7 @@ export default function SettingsPage() {
           </RulesFold>
 
           <section className="settings-section">
-            <h3>币种兑换（USDT ↔ USDC）</h3>
+            <h3>币种兑换（交易账户 · USDT ↔ USDC）</h3>
             <div className="settings-fields">
               <div className="field">
                 <label htmlFor="convertDir">方向</label>