fix: remove vhs/ from repo, add to gitignore

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: hi-lei

.gitignore

@@ -358,7 +358,5 @@ tmp/
 temp/
 tmp-test-*/
 
-# VHS generated output (keep .tape files, ignore output)
-vhs/*.gif
-vhs/*.mp4
-vhs/*.webm
+# VHS demo recordings
+vhs/