docs: use local video assets for READMEs

README.md

@@ -9,7 +9,7 @@
 
 [繁體中文使用說明](USAGE_zh.md)
 
-<video src="https://blog-assets.firstsun.org/video/obsidian-plugins/git-file-sync-en.webm" width="100%" controls autoplay loop muted playsinline></video>
+<video src="imgs/git-file-sync-en.webm" width="100%" controls autoplay loop muted playsinline></video>
 
 ![sync-status](imgs/sync-status.png)
 *The Sync Status View provides a clear overview of your files, allowing you to selectively push, pull, or view diffs for modified files.*

USAGE_zh.md

@@ -1,6 +1,6 @@
 # Git File Sync 使用說明書
 
-<video src="https://blog-assets.firstsun.org/video/obsidian-plugins/git-file-sync-zh.webm" width="100%" controls autoplay loop muted playsinline></video>
+<video src="imgs/git-file-sync-zh.webm" width="100%" controls autoplay loop muted playsinline></video>
 
 本指南將引導您如何使用 Git File Sync 插件，在行動裝置與桌面電腦之間，透過 GitLab 或 GitHub 輕鬆同步您的筆記。