docs: replace demo video with webp screenshot

Use a static WebP cover image in README instead of an embedded video.
Remove the mp4 asset to keep the repository lean.

Author: joaner

README.md

@@ -11,7 +11,9 @@
 Supports **MCAP**, **ROS 1 bag**, **ROS 2 db3**, **HDF5**, and **BVH** files. Available as a standalone SPA (zero-install, runs at [rosview.com](https://rosview.com)) or as an embeddable npm package.
 
 <p align="center">
-  <video src="https://raw.githubusercontent.com/ioai-tech/rosview/refs/heads/main/docs/assets/rosview-demo.mp4" autoplay loop muted playsinline width="920"></video>
+  <a href="https://rosview.com">
+    <img src="docs/assets/rosview-demo.webp" alt="ROSView demo — Realman pick and place" width="920">
+  </a>
 </p>
 
 ---

README.zh.md

@@ -9,7 +9,9 @@
 支持 **MCAP**、**ROS 1 bag**、**ROS 2 db3**、**HDF5** 与 **BVH** 文件。可作为独立 SPA（零安装，访问 [rosview.com](https://rosview.com)）或作为可嵌入的 npm 包使用。
 
 <p align="center">
-  <video src="https://raw.githubusercontent.com/ioai-tech/rosview/refs/heads/main/docs/assets/rosview-demo.mp4" autoplay loop muted playsinline width="920"></video>
+  <a href="https://rosview.com">
+    <img src="docs/assets/rosview-demo.webp" alt="ROSView 演示 — Realman pick and place" width="920">
+  </a>
 </p>
 
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