[Feature Request]: Encrypt Password

### 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

Password is stored in clear text.

### Proposed Solution

Encrypt password.

### Alternatives Considered

None.

### Issue Labels

improvement to existing feature

### Additional Information

_No response_

No file, test, or entry point is named. Start by locating where FreeTube stores the password and how that value is used; clarify the encryption design, key handling, migration path, and completion criteria before implementation.

Written by the indexing model from the issue text.