Play episodes selected from the Android Auto browse tree

[mapitman]

Goal

Tapping a playable item in the Android Auto browse tree (issue #250) needs to actually start playback, going through the same resolution logic (download-path vs. streaming URL, mobile-data gating, start position, volume boost) that PlaybackController/PlaybackService already use for in-app playback.

Scope

• Handle MediaSession.Callback.onAddMediaItems (or onSetMediaItems) so a bare MediaItem from the browse tree (carrying only a media ID) gets resolved through PlaybackMediaItemFactory.resolve into a real playable item, the same way PlaybackService.playNextQueued already does for queue auto-advance.
• Tapping an episode not in Next Up should behave sensibly — either start it standalone or add-and-play it at the front of the queue (decide based on what feels right relative to existing in-app "play now" semantics; check PlaybackController for the existing pattern before inventing a new one).
• Apply the same mobile-data streaming gate as in-app playback (issue Warn and let the user override at play-time instead of a blanket disable-streaming-on-mobile-data toggle #222) — Auto has no UI to show a confirmation dialog from, so this should behave like PlaybackService's non-interactive auto-advance path (forceAllowStreaming = false), not silently bypass the gate.

Testing

From the Desktop Head Unit, tap an episode in a feed's Auto browse list and confirm it starts playing, position/volume-boost/speed are applied correctly, and it appears correctly in Auto's now-playing screen (title, artist, artwork, transport controls).

[mapitman]

Resolved by #254.