fix(plex): keep compatible audio on capped transcodes (#1845)

`maxVideoBitrate` budgets the whole stream, so a capped transcode forced
even profile-compatible audio down to low-rate AAC (measured on Plex
1.43: EAC3 5.1 640k became 360k AAC). The client profile already carries
the video cap through `add-limitation(video.bitrate)`, so drop the
redundant `maxVideoBitrate` param and send `directStreamAudio=1`: the
video stays capped per preset while audio in the codecs the profile
declares (aac/ac3/eac3/mp3) is copied through untouched. Audio the HLS
target cannot carry still transcodes as before.

lib/services/plex_client.dart

@@ -3001,10 +3001,9 @@ class PlexClient
       'subtitleSize': '100',
       'audioBoost': '100',
       'location': 'lan',
-      if (!isOriginal && preset.videoBitrateKbps != null) 'maxVideoBitrate': preset.videoBitrateKbps.toString(),
       'addDebugOverlay': '0',
       'autoAdjustQuality': '0',
-      'directStreamAudio': '0',
+      'directStreamAudio': '1',
       'mediaBufferSize': '102400',
       'session': transcodeSessionId,
       if (offset != null && offset > Duration.zero) 'offset': (offset.inMilliseconds / 1000).toStringAsFixed(6),