Add default episode sort option

### What problem does this address?

As far as I know this option is not available.

When I subscribe to a new podcast, the first I always do is to sort the episodes from newest to oldest. It would be nice to have the option to change the default from "oldest to newest" to "newest to oldest".

### What is your proposed solution?

Add an option under "general -> defaults" for something like "episode sorting", so that episodes can be sorted to "newest to oldest" by default.

### Did you search for existing feature suggestions?

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

Start by locating the General → Defaults settings screen and the episode-list sorting entry point. Trace how the default preference is stored and applied; done means a selectable episode-sorting default persists and new podcast episode lists use it, with coverage for both orders.

Written by the indexing model from the issue text.