iOS 1.0 RC 2: Plex streams under upload caps, shuffle and album radio stations, Recently Added list, photo covers, crossfade

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

ios/Stemify/Plex/MediaServer.swift

@@ -57,6 +57,8 @@ protocol MediaSource: AnyObject, Sendable {
     func timeline(_ track: Track, state: String, positionMs: Int64) async
     func artUrl(_ thumb: String?, px: Int) -> URL?
     func partUrl(_ partKey: String) -> URL?
+    /// The URL to stream a track's file from, after any setup the server needs for playback.
+    func streamUrl(_ ratingKey: String, partKey: String) async -> URL?
     /// Music libraries on the server, for the picker in Settings.
     func musicSections() async throws -> [MusicSection]
 }