Retire cancelled playback sessions and preserve VOD content time

Adapted from MikaelKW/nodecast-tv-plus playback lease work beginning at 43a58c7685f541498663b827c4b9d6b3753e7202. Reject superseded requests, release on cancellation, bound live restart attempts and await FFmpeg close before deleting cache.

Co-authored-by: Mikael <mikaelkwessel@gmail.com>

server/routes/remux.js

@@ -166,7 +166,7 @@ router.get('/', async (req, res) => {
     });
 
     // Cleanup on client disconnect
-    req.on('close', () => {
+    res.on('close', () => {
         console.log('[Remux] Client disconnected, killing FFmpeg process');
         ffmpeg.kill('SIGKILL');
     });