Add a video-guide recorder for the UI (Settings tabs, Event Manager tabs, Schedule panel)

CDP screencast -> ffmpeg -> MKV, driven against the same isolated server/browser pattern
the test suite already uses. Recorded three short clips demonstrating this session's tab
and schedule features; output goes to the gitignored video-guides/ folder rather than the
repo since these are sizeable binaries.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

.gitignore

@@ -17,3 +17,4 @@ Thumbs.db
 coverage/
 dist/
 tmp/
+video-guides/