feat: replace x-code icon with high-res xcode icon via URL import

Replace the old low-res x-code inline SVG (7.6KB) with a new high-res
xcode.svg (286KB) loaded via Vite URL import. Update all three provider
preset files to reference the new icon name.

src/config/codexProviderPresets.ts

@@ -331,7 +331,7 @@ requires_openai_auth = true`,
     category: "third_party",
     isPartner: true, // 合作伙伴
     partnerPromotionKey: "x-code", // 促销信息 i18n key
-    icon: "x-code",
+    icon: "xcode",
     iconColor: "#000000",
   },
   {