- Add ActiveDownloadItem data class to represent a download in progress
- Add observeActiveDownloads() to MediaDownloadManager, polling the Media3
download index every 500ms on Dispatchers.IO for reliable real-time progress
(listener callbacks alone do not fire on every progress update)
- DownloadsViewModel exposes activeDownloads (StateFlow) and cancelDownload();
the completed downloads flow filters out items currently in progress
- DownloadsContent shows a "Downloading" section with thumbnail, title,
progress bar + percentage, and a cancel button above the completed grid
- Remove RoomMediaLocalDataSource dependency from InMemoryMediaRepository;
libraries, movies, series, and episodes are now held in MutableStateFlows
- observeSeriesWithContent derives from _series flow via map {}
- updateWatchProgress mutates _movies / _episodes in-memory
- ensureSeriesContentLoaded checks and updates _series in-memory
- Reorganize Room package: move entities/DAOs from local/room to room/entity and room/dao
