Add .m4a audio preview support

[gogo25171]

Feature request

Please add support for .m4a files in the preview extension.

Currently, video/audio preview works for several media formats, but .m4a files are not recognized or playable.

Expected behavior

• .m4a files should open in the preview player
• Playback controls should work the same way as for other supported audio/video formats

Why this would help

.m4a is a very common audio format, especially for recordings and exported audio files from Apple devices and many applications.

Thanks for the extension!