[Enhancement] Mark videos as watched on any page instead of just subscriptions.

[TangentFoxy]

Is your enhancement request related to a problem? Please describe.
I rely on an external indication to remind me of videos I've already watched, and sometimes those videos are very far back in time, so finding them in the subscription feed to mark as watched is impractical. Opening a video does mark it as watched (when you have that enabled), but only when an instance is fully functioning normally. Even when YouTube changes harm my ability to use Invidious, I still mark which videos I have watched using it. I would like to be able to do this at least on channels, but preferably anywhere.

Describe the solution you'd like
The system for marking videos as watched on subscriptions should be available on channels, and everywhere else videos are displayed.

Describe alternatives you've considered

• I could try to find the videos in the subscription feed, but I have too many subscriptions for that, and the instance I'm on doesn't go that much farther back than when I created my account there.
• I could manually add IDs to a JSON file and import that, but that's messy and involved.
• I could just fix this when the blocking isn't so bad, but that's unreliable, manual, and tedious.

Additional context
n/a