Feature: Create Folders/Lists with unsubscribed Podcasts

### What problem does this address?

I want to be able to create Lists/Folders of Podcasts that I am not subscribed to. This could be useful in multiple cases.

- I want to listen to a Podcast but am currently not.
- I have listened to a Podcast and want to "archive" it, so I don't need to get updated on new episodes.
- I stopped listening to a Podcast, but want to save it to look at it later on.

These things are especially useful for Fiction Podcasts that usually only get listened to once and mostly don't get any later updates, so syncing them can be wasteful.

### What is your proposed solution?

Being able to make Folders/Lists that include Podcasts that I am not subscribed to. Just to have them on the homescreen/accessible quickly. This means I don't need to subscribe to many Podcasts to simply save them for later, or keep them after having listened to them. This would mean that those Podcasts that I don't actually to listen at the moment don't need to synced at all and can be handled just like Podcasts I am not subscribed to (because I am not).

### Did you search for existing feature suggestions?

- [X] I have searched for existing feature suggestions.

The issue names no files, tests, or entry points. Start by reviewing the existing folder/list and subscription flows, then clarify how unsubscribed podcasts should appear and behave in saved, archived, and fiction-podcast cases. Done means users can access those podcasts from a folder or list without subscribing or syncing them.

Written by the indexing model from the issue text.