docs: add new English and Chinese app screenshots and update READMEs to reference them.

README.md

@@ -1,9 +1,10 @@
 # Caption Trans
 
-![App Screenshot](screenshot_placeholder.png)
-
 [中文版](README_zh.md)
 
+## App Screenshot
+![App Screenshot](screenshots/screenshot_en.jpg)
+
 A one-stop video subtitle translation tool. It extracts subtitles locally using Whisper and accurately translates them into the target language using LLM.
 Currently, it supports OpenAI, Google Gemini, DeepSeek, Ollama, and other API services compatible with the OpenAI interface.
 

README_zh.md

@@ -1,8 +1,9 @@
 # Caption Trans
 
-![应用截图](screenshot_placeholder.png)
+[English Version](README.md)
 
-[English](README.md)
+## 应用截图
+![应用截图](screenshots/screenshot_zh.jpg)
 
 一站式视频字幕翻译软件。通过本地 Whisper 提取字幕，并使用 AI 将其准确翻译为目标语言。
 目前支持OpenAI、Google Gemini、DeepSeek、Ollama 等兼容 OpenAI 的 API 服务。