fix(agent): honor configured auto image model for image intents

lib/ai/model-router.ts

@@ -143,17 +143,28 @@ export async function routeToModel(params: {
     );
 
     if (configuredModel) {
+      const isImageIntent = intent === "image_edit" || intent === "image_gen";
       const matchesVision = !config.requireVision || configuredModel.model.supportsVision;
       const matchesImageGen = !config.requireImageGen || configuredModel.model.supportsImageGen;
+      const allowImageIntentWithImageGenOnly =
+        isImageIntent && configuredModel.model.supportsImageGen;
 
-      if (matchesVision && matchesImageGen) {
+      if ((matchesVision && matchesImageGen) || allowImageIntentWithImageGenOnly) {
+        const reason = allowImageIntentWithImageGenOnly && !matchesVision
+          ? `管理员配置的默认模型（按生图能力优先）→ ${configuredModel.model.displayName}`
+          : `管理员配置的默认模型 → ${configuredModel.model.displayName}`;
         console.log("[Model Router] ✅ Using configured default model:", configuredModel.model.displayName);
+        if (allowImageIntentWithImageGenOnly && !matchesVision) {
+          console.log(
+            "[Model Router] ℹ️ Configured default model does not support vision, but image intent can reuse Agent analysis and keep admin default image model."
+          );
+        }
         return {
           id: configuredModel.model.id,
           displayName: configuredModel.model.displayName,
           providerType: configuredModel.provider.type,
           modelId: configuredModel.model.modelId,
-          reason: `管理员配置的默认模型 → ${configuredModel.model.displayName}`,
+          reason,
         };
       }