fix: update pricing details for image and poster generation

- Adjust pricing for image generation from $0.4 to $0.004 per image.
- Update pricing for poster generation from $0.4 to $0.04 per poster.
- Ensure accurate pricing reflects current service costs.

Author: harryisfish

content/docs/user-guide/pricing.mdx

@@ -24,8 +24,8 @@ title: Pricing | 定价 (WIP)
 | 多平台发布 | 免费 | 浏览器扩展、Extension API、Restful API 均免费 |
 | Reader、SERP | $0.2/1M Tokens | 按 Token 计费 |
 | DeepSeek V3 | Input: $0.27/1M Tokens<br/>Output: $1.1/1M Tokens | 输入输出分别计费,定价同步 DeepSeek 官网 |
-| 图片生成 | $0.4/image | 单张图片计费 |
-| 海报生成 | $0.4/poster | 单张海报计费 |
+| 图片生成 | $0.004/image | 单张图片计费 |
+| 海报生成 | $0.04/poster | 单张海报计费 |
 | 文件托管 | $0.04/1GB | 按访问流量计费 |
 
 ## 最低消费