🎬 Mixer Just Got Smarter

I slightly improved the logic of mixer.playphrase.me to remove a common confusion. Some users were downloading already-processed karaoke videos from playphrase.me and then sending them back into the mixer — which resulted in an empty file. Now the mixer understands what you want: either combine already generated karaoke clips into one big video, or take original clips and generate the karaoke version in batch. Same final result, two flexible workflows — generate individually first or keep originals and process everything at once. And one more nice bonus: if subscribers merge karaoke videos into one, the final export won’t include the mixer watermark on top.