docs(readme): replace demo link with embedded video for better accessibility

Author: doniaskima

README.md

@@ -8,7 +8,9 @@ It keeps a local SQLite database with an FTS5 index for fast search. It does **n
 
 ## Demo
 
-## ▶️ [Watch CmdBook in action](record/record.mov)
+<video src="record/record.mov" width="800" controls muted>
+  Your browser does not support the video tag.
+</video>
 
 ## Features