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/tools/gentest.go

@@ -0,0 +1,49 @@
+//go:build ignore
+
+package main
+
+import (
+	"context"
+	"fmt"
+	"os"
+
+	"gen2d/internal/config"
+	"gen2d/internal/service"
+)
+
+func main() {
+	cfg := config.Load()
+
+	// 清空 API key 强制走 mock
+	cfg.ImageGen.APIKey = ""
+	service.InitImageGenConfig(cfg.ImageGen)
+	service.InitLLMConfig(cfg.LLM)
+
+	in := service.PipelineInput{
+		AssetType: "sprite",
+		Prompt:    "a cute cat warrior with golden armor",
+		Tags:      []string{"pixel art", "fantasy", "16-bit"},
+		Params: service.AssetParams{
+			Resolution: 816,
+			Frames:     service.FrameParams{Directions: 4, FramesPerDirection: 1},
+			Format:     "individual",
+		},
+	}
+
+	output, err := service.RunPipeline(context.Background(), in)
+	if err != nil {
+		fmt.Fprintf(os.Stderr, "error: %v\n", err)
+		os.Exit(1)
+	}
+
+	os.MkdirAll("test_output", 0755)
+	for i, a := range output.Assets {
+		fname := fmt.Sprintf("test_output/gen_%d.%s", i, a.Format)
+		if err := os.WriteFile(fname, a.Data, 0644); err != nil {
+			fmt.Fprintf(os.Stderr, "write %s: %v\n", fname, err)
+			os.Exit(1)
+		}
+		fmt.Printf("saved %s (%d bytes)\n", fname, len(a.Data))
+	}
+	fmt.Printf("metadata: %+v\n", output.Metadata)
+}