Add warning when streaming episodes on watch

### What problem does this address?

Streaming episodes on the watch can be a poor user experience if the network connection is not really good. It is also really easy to start streaming an episode that has not been downloaded if you're not careful.

### What is your proposed solution?

It may be a good idea to give a warning when a user begins streaming an episode so they realize they're streaming an episode and we could give them an option to download the episode in that warning. We could add a toggle in the settings for the user to turn this warning off if they want.

### Did you search for existing feature suggestions?

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

The issue names no files or tests. Start by locating the Android entry point for starting playback of an episode that is not downloaded, then inspect the existing settings and download flows. Confirm the warning, download action, and opt-out behavior with maintainers before implementation; done means the agreed behavior works for streaming episodes and the setting is respected.

Written by the indexing model from the issue text.