feat(image): support arbitrary size and aspect ratio shortcuts for doubao generate

- --size now accepts free-form values (2K, 3K, 4K, 2304x1728, etc.)
  instead of a fixed [1K, 2K] choice.
- Add --ratio shortcut (1:1, 4:3, 3:4, 16:9, 9:16) mapping to pixel sizes.
- When both --size and --ratio are given, --size takes priority.
- Default remains 2K when neither is specified.

bin/commands/image.py

@@ -187,15 +187,25 @@ def compress_images(files, target_mb, max_width, quality, suffix, dry_run):
             click.echo(f"Compressed: {img_file} -> {output} ({size_mb:.2f} MB)")
 
 
+_RATIO_MAP = {
+    "1:1": "1024x1024",
+    "4:3": "1024x768",
+    "3:4": "768x1024",
+    "16:9": "1280x720",
+    "9:16": "720x1280",
+}
+
+
 @image.command("generate")
 @click.argument("prompt", required=False)
 @click.option("-f", "--file", type=click.Path(exists=True), help="从文件读取 prompt")
-@click.option("-s", "--size", default="2K", type=click.Choice(["1K", "2K"]), help="图片尺寸")
+@click.option("-s", "--size", help='图片尺寸 (如 2K, 3K, 4K 或 2304x1728)')
+@click.option("-r", "--ratio", type=click.Choice(list(_RATIO_MAP.keys())), help="快捷比例 (1:1, 4:3, 3:4, 16:9, 9:16)")
 @click.option("-o", "--output", help="保存路径（默认只输出 URL）")
 @click.option("--no-watermark", is_flag=True, help="不添加豆包水印")
 @click.option("--b64", is_flag=True, help="使用 b64_json 格式获取图片数据")
 @handle_errors
-def generate_image_cmd(prompt, file, size, output, no_watermark, b64):
+def generate_image_cmd(prompt, file, size, ratio, output, no_watermark, b64):
     """使用豆包/Seedream 模型生成图片。"""
     from openai import OpenAI
 
@@ -209,6 +219,11 @@ def generate_image_cmd(prompt, file, size, output, no_watermark, b64):
         click.echo("Error: apikey_ark not set. Run: mytoolkit env set apikey_ark <value>", err=True)
         raise click.Abort()
 
+    if size and ratio:
+        click.echo("Warning: --size 和 --ratio 同时指定，--size 优先", err=True)
+
+    resolved_size = size or (ratio and _RATIO_MAP[ratio]) or "2K"
+
     client = OpenAI(
         base_url="https://ark.cn-beijing.volces.com/api/v3",
         api_key=api_key,
@@ -217,7 +232,7 @@ def generate_image_cmd(prompt, file, size, output, no_watermark, b64):
     resp = client.images.generate(
         model="doubao-seedream-5-0-260128",
         prompt=prompt,
-        size=size,
+        size=resolved_size,
         response_format="b64_json" if b64 else "url",
         extra_body={"watermark": not no_watermark},
     )