[Feature Request]: Transient "hide watched" toggle

### Guidelines

- [X] I have searched the issue tracker for [open](https://github.com/FreeTubeApp/FreeTube/issues?q=is%3Aopen+is%3Aissue) and [closed](https://github.com/FreeTubeApp/FreeTube/issues?q=is%3Aissue+is%3Aclosed) issues that are similar to the feature request I want to file, without success.
- [X] I have searched the [documentation](https://docs.freetubeapp.io/) for information that matches the description of the feature request I want to file, without success.
- [X] This issue contains only one feature request.

### Problem Description

As a user, I sometimes want to hide watched videos in my subscriptions only sometimes. Rather than have to enable and disable a permanent setting, I would like to be able to do it on a whim and have it revert when it's no longer desired.

### Proposed Solution

Implement transient toggle switch somewhere on the Subscriptions page (like the `ft-refresh-widget` or the top of the page) that overrides the "Hide Videos on Watch" preference until the route is changed.

### Alternatives Considered

Have the toggle override the default setting for the session instead of just until route change.

### Issue Labels

ease of use improvement, improvement to existing feature

### Additional Information

_No response_

Start at the Subscriptions page and inspect the ft-refresh-widget or page-level controls, then trace the existing "Hide Videos on Watch" preference. Done means a transient toggle can override that preference on the page and automatically revert when the route changes; verify both enabled and disabled preference states.

Written by the indexing model from the issue text.