单笔期权默认改为币本位；未配置时按coin处理

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

lib/env/env_schema.py

@@ -167,8 +167,8 @@ SELECT_OPTIONS: dict[str, tuple[tuple[str, str], ...]] = {
         ("options_options", "期期对冲"),
     ),
     "OKX_OPTIONS_MARGIN_MODE": (
-        ("usdc", "USDC(USDⓈ权利金)"),
         ("coin", "币本位(USDT买币桥)"),
+        ("usdc", "USDC(USDⓈ权利金)"),
     ),
     "HEDGE_PLAN_OPTION_PRIMARY": (
         ("true", "以期权为主"),

lib/env/env_ui_manifest.py

@@ -146,7 +146,7 @@ _OPTIONS_SECTION: dict[str, Any] = {
         (
             "OKX_OPTIONS_MARGIN_MODE",
             "单笔期权本位",
-            "usdc=USDⓈ权利金;coin=币本位+USDT买币桥。有持仓/半成品桥时勿切换;改后需重启",
+            "usdc=USDⓈ权利金;coin=币本位+USDT买币桥(默认)。有持仓/半成品桥时勿切换;改后需重启",
         ),
         (
             "OKX_OPTIONS_TRADE_BUDGET_USDC",