[Feature Request]: allow removing videos from playlist through Add to Playlist menu

### Guidelines

- [x] I have [searched the issue tracker for open and closed issues](https://github.com/FreeTubeApp/FreeTube/issues?q=is%3Aissue+sort%3Arelevance-desc) 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.
- [x] I have read and agree to follow the [rules](https://docs.freetubeapp.io/community/rules/).

### Problem Description

you can add a video to a playlist through the plus menu which is there on every video. after clicking the plus, you can add a video to any playlists you want, all at once. you can check and uncheck playlists to add the video to before saving. however, through the plus menu, you cant remove a video from a playlist it was already added to, there is no unchecking videos that have already been added.

### Proposed Solution

allow unchecking videos from playlists they are already added to.

### Alternatives Considered

none that are convenient.

### Issue Labels

ease of use improvement, improvement to existing feature

### FreeTube Version

freetube_0.25.1_beta_amd64.deb

### Operating System Version

Linux Mint 22.3 - Cinnamon 64-bit

### Installation Method

.deb

### Upload screenshots or videos

_No response_

### Additional Information

_No response_

The issue does not name files or tests. Start by locating the Add to Playlist or plus-menu entry point and tracing the existing playlist-selection flow. Done means an already-selected playlist can be unchecked to remove the video, while adding to selected playlists continues to work.

Written by the indexing model from the issue text.