feat: 添加图生图 DTO

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

backend/gateway/dto/image_dto.go

@@ -0,0 +1,34 @@
+package dto
+
+// ImageGenerationRequest MiniMax 图生图请求
+type ImageGenerationRequest struct {
+    Model            string              `json:"model" binding:"required"`
+    Prompt           string              `json:"prompt" binding:"required"`
+    AspectRatio      string              `json:"aspect_ratio"`
+    SubjectReference []SubjectReference  `json:"subject_reference"`
+    N                int                 `json:"n"` // 1-4
+}
+
+type SubjectReference struct {
+    Type      string `json:"type"`
+    ImageFile string `json:"image_file"`
+}
+
+// ImageJobResponse 图生图任务响应
+type ImageJobResponse struct {
+    JobID       string   `json:"job_id"`
+    Status      string   `json:"status"`
+    Progress    int      `json:"progress"`
+    Images      []string `json:"images,omitempty"`
+    ErrorMsg    string   `json:"error_msg,omitempty"`
+    CreatedAt   int64    `json:"created_at"`
+    UpdatedAt   int64    `json:"updated_at"`
+    CompletedAt int64    `json:"completed_at,omitempty"`
+}
+
+// ImageJobCreateResponse 创建任务响应
+type ImageJobCreateResponse struct {
+    JobID     string `json:"job_id"`
+    Status    string `json:"status"`
+    CreatedAt int64  `json:"created_at"`
+}