feat: AI 提供商列表明文回传默认模型，并按类型回落模型名

ApiSecret 实际承载文字主模型，列表不再脱敏；未配置时 Chat 按厂商默认模型回落。

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

src/Oms.Application/Dtos/Ai/AiDtos.cs

@@ -16,6 +16,9 @@ public class AiProviderOutput
 
     public string? ApiKey { get; set; }
 
+    /// <summary>
+    /// 默认模型名（历史字段名 ApiSecret，实际不当密钥脱敏）。
+    /// </summary>
     public string? ApiSecret { get; set; }
 
     public bool IsDefault { get; set; }
@@ -39,6 +42,9 @@ public class AiProviderSaveInput
 
     public string? ApiKey { get; set; }
 
+    /// <summary>
+    /// 默认文字模型 ID；空表示保持原值。
+    /// </summary>
     public string? ApiSecret { get; set; }
 
     public bool IsDefault { get; set; }

src/Oms.Application/Services/Ai/AiService.cs

@@ -127,7 +127,8 @@ public class AiService : ApplicationService
         DisplayName = entity.DisplayName,
         BaseUrl = entity.BaseUrl,
         ApiKey = maskSecret ? MaskSecret(entity.ApiKeyEnc) : entity.ApiKeyEnc,
-        ApiSecret = maskSecret ? MaskSecret(entity.ApiSecretEnc) : entity.ApiSecretEnc,
+        // ApiSecret 实际承载默认模型名，列表需明文回传以便卡片展示/编辑
+        ApiSecret = entity.ApiSecretEnc,
         IsDefault = entity.IsDefault,
         Enabled = entity.Enabled
     };

src/Oms.Application/Shared/AiLlmClient.cs

@@ -82,6 +82,10 @@ public class AiLlmClient
 
         var model = modelOverride ?? provider.ApiSecretEnc;
         if (string.IsNullOrWhiteSpace(model))
+        {
+            model = DefaultModelForProviderType(provider.ProviderType);
+        }
+        if (string.IsNullOrWhiteSpace(model))
         {
             throw new BusinessException($"请先配置 {provider.DisplayName} 的模型名（ApiSecret 字段）或在请求中传入 model");
         }
@@ -256,6 +260,19 @@ public class AiLlmClient
 
         return body.Length <= 300 ? body : body[..300];
     }
+
+    /// <summary>
+    /// 未配置 ApiSecret（模型名）时按提供商类型回落默认模型。
+    /// </summary>
+    private static string? DefaultModelForProviderType(string? providerType) =>
+        (providerType ?? string.Empty).Trim().ToLowerInvariant() switch
+        {
+            "chatgpt" => "gpt-4o-mini",
+            "doubao" => "doubao-1-5-pro-32k-250115",
+            "deepseek" => "deepseek-chat",
+            "zhipu" => "glm-5.1",
+            _ => null
+        };
 }
 
 public static class AiLlmServiceExtensions