fix(inference): 修正文生图 API 调用参数，支持动态分辨率

- 去掉 response_format 参数（API 默认返回 URL，自动下载）
- Resolution 参数覆盖 API 调用尺寸（不再仅 mock 路径生效）
- parseImageResponse 改为动态 width/height 入参
- 新增 tools/gentest.go 生成测试脚本
- .gitignore 忽略 test_output/

backend/internal/service/inference.go

@@ -36,7 +36,6 @@ type imageGenRequest struct {
 	Prompt         string  `json:"prompt"`
 	N              int     `json:"n,omitempty"`
 	Size           string  `json:"size,omitempty"`
-	ResponseFormat string  `json:"response_format,omitempty"`
 	Steps          int     `json:"steps,omitempty"`
 	CFGScale       float64 `json:"cfg_scale,omitempty"`
 }
@@ -57,7 +56,12 @@ func GenerateImages(ctx context.Context, prompt string, params AssetParams) ([]G
 	}
 
 	if imgCfg.APIKey != "" {
-		return callImageGenAPI(ctx, prompt, count)
+		width, height := imgCfg.Width, imgCfg.Height
+		if params.Resolution > 0 {
+			width = params.Resolution
+			height = params.Resolution
+		}
+		return callImageGenAPI(ctx, prompt, count, width, height)
 	}
 
 	size := params.Resolution
@@ -69,13 +73,12 @@ func GenerateImages(ctx context.Context, prompt string, params AssetParams) ([]G
 }
 
 // callImageGenAPI 调用 OpenAI 兼容的 Images API，返回生成的图片。
-func callImageGenAPI(ctx context.Context, prompt string, count int) ([]GeneratedImage, error) {
+func callImageGenAPI(ctx context.Context, prompt string, count, width, height int) ([]GeneratedImage, error) {
 	reqBody := imageGenRequest{
 		Model:          imgCfg.Model,
 		Prompt:         prompt,
 		N:              count,
-		Size:           fmt.Sprintf("%dx%d", imgCfg.Width, imgCfg.Height),
-		ResponseFormat: "b64_json",
+		Size:           fmt.Sprintf("%dx%d", width, height),
 	}
 	if imgCfg.Steps > 0 {
 		reqBody.Steps = imgCfg.Steps
@@ -108,7 +111,7 @@ func callImageGenAPI(ctx context.Context, prompt string, count int) ([]Generated
 		return nil, fmt.Errorf("image gen api error %d: %s", resp.StatusCode, string(b))
 	}
 
-	return parseImageResponse(ctx, resp.Body)
+	return parseImageResponse(ctx, resp.Body, width, height)
 }
 
 // ======================== 图片编辑 API ========================
@@ -138,7 +141,6 @@ func callImageEditAPI(ctx context.Context, imageData []byte, prompt string, coun
 	writer.WriteField("model", imgCfg.Model)
 	writer.WriteField("n", strconv.Itoa(count))
 	writer.WriteField("size", fmt.Sprintf("%dx%d", imgCfg.Width, imgCfg.Height))
-	writer.WriteField("response_format", "b64_json")
 
 	if err := writer.Close(); err != nil {
 		return nil, fmt.Errorf("close multipart writer: %w", err)
@@ -164,11 +166,11 @@ func callImageEditAPI(ctx context.Context, imageData []byte, prompt string, coun
 		return nil, fmt.Errorf("image edit api error %d: %s", resp.StatusCode, string(b))
 	}
 
-	return parseImageResponse(ctx, resp.Body)
+	return parseImageResponse(ctx, resp.Body, imgCfg.Width, imgCfg.Height)
 }
 
 // parseImageResponse 解析 OpenAI 兼容的图片生成/编辑响应体。
-func parseImageResponse(ctx context.Context, r io.Reader) ([]GeneratedImage, error) {
+func parseImageResponse(ctx context.Context, r io.Reader, width, height int) ([]GeneratedImage, error) {
 	var genResp imageGenResponse
 	if err := json.NewDecoder(r).Decode(&genResp); err != nil {
 		return nil, fmt.Errorf("decode response: %w", err)
@@ -195,8 +197,8 @@ func parseImageResponse(ctx context.Context, r io.Reader) ([]GeneratedImage, err
 		}
 		images = append(images, GeneratedImage{
 			Data:   data,
-			Width:  imgCfg.Width,
-			Height: imgCfg.Height,
+			Width:  width,
+			Height: height,
 			Format: "png",
 		})
 	}