Count real listening time instead of full track duration

"Listening time this week" summed the full duration of every track whose
stream ticket was issued, so pressing play and skipping counted the whole
song. Playback is now measured on the client and reported to the API.

Backend:
- ListeningHistory gains PlayedSeconds, LastProgressAt and IsCounted
  (migration TrackPlayedSeconds marks existing rows as counted).
- /tracks/{id}/stream returns a listenId; new
  PUT /tracks/listens/{listenId}/progress stores the accumulated seconds,
  capped by track duration and elapsed wall-clock time, monotonic and
  owner-only.
- A listen counts once it reaches min(30s, 50% of the track). Weekly
  stats, streak, recent history/albums, mixes and listensCount only use
  counted listens; seconds sum PlayedSeconds.
- ListeningHistoryCleanupJob (daily) deletes uncounted listens older
  than 8 days.

web-player:
- ListenTracker accumulates played time (seeks are ignored) and flushes
  on pause, track change, ended, every 30s, and on pagehide.
- Proxy route /api/listens/[id]/progress; repeat starts a new listen per
  loop.

backend/Core/Musify.Infrastructure/Jobs/DailyMixGenerationJob.cs

@@ -15,6 +15,7 @@ namespace Musify.Infrastructure.Jobs
         {
             var userIds = await database.ListeningHistories
                 .AsNoTracking()
+                .Where(history => history.IsCounted)
                 .Select(history => history.UserId)
                 .Distinct()
                 .ToListAsync(cancellationToken);

backend/Core/Musify.Infrastructure/Jobs/ListeningHistoryCleanupJob.cs

@@ -0,0 +1,13 @@
+using Mediator;
+using Musify.Application.Tracks;
+
+namespace Musify.Infrastructure.Jobs
+{
+    public class ListeningHistoryCleanupJob(IMediator mediator)
+    {
+        public async Task RunAsync(CancellationToken cancellationToken)
+        {
+            await mediator.Send(new DeleteStaleUncountedListensCommand(), cancellationToken);
+        }
+    }
+}