Video streams: provide live status information

Expanding on some suggestions in #800, we should support:

- [x] an optional debug/quality overlay in the Video widget, showing FPS, bitrate, and dropped frames
- [x] optional recording/logging of those values
- relevant to #621 if logging to the subtitle files
- even if it's just stored in Cockpit's logs and saved/accessed separately, that should still be much faster to check than scrubbing through a long video recording
- if we do this approach then we should probably run an automated video quality check after each recording, and notify of potential problem periods and/or provide a graph of video health over time (which could potentially replace `#800`)
- [ ] a "video health" mini-widget, tied to an incoming video stream in the same way the recording widget is
- I'm imagining a video symbol (per connected stream) in the top right mini-widget bar, with the symbol colour/icon based on thresholds for quality, e.g.
- green video-camera --> all good
- yellow video-camera --> some dropped frames, or inconsistent FPS/bitrate
- yellow video-camera with black exclamation --> bad enough that investigation is recommended
- red video-camera with black exclamation --> poor quality - footage unlikely to be usable
- grey video-camera with red cross --> camera stream not detected as available
- status changes could also create text notifications for the notification bar
- hovering over the icon should show
- status highlights (i.e. the cause of the status, like "low FPS, 21.3/25")
- any corresponding recommendations (check power supply, camera temperature, etc), and
- an obvious marker on any visible players of the video stream it's connected to (e.g. a red border on the widget(s), or fading/blurring all the other widgets)
- clicking on the icon should either
- open a pop-up showing the video quality info + common troubleshooting tips, or
- toggle the debug overlay for any corresponding video widgets that are using that stream

The issue names the Video widget, recording widget, incoming video streams, and the top-right mini-widget bar; locate those entry points first and review how streams are represented. Define the requested quality states, thresholds, notifications, hover details, and click behavior before implementing the unchecked video-health mini-widget. Done means the widget reflects stream health and connects to the relevant video players as described.

Written by the indexing model from the issue text.