Dolby audio on Android, and macOS opens again

Two platforms that could fail before a film ever started.

Fixes

Films with Dolby audio play on Android. A device would report that it could decode E-AC-3, accept the track, and then reject the very first frame - fourteen milliseconds in, picture up and no sound, on a link that played everywhere else. Ventic now carries its own FFmpeg decoder and retries with it when the device's one gives up. The device decoder is still tried first, so passthrough to a receiver is untouched.
macOS opens again. 0.5.1 was built on a machine newer than the Macs it shipped to, and the libraries inside the app refused to load there - it was killed before it drew anything. The build is pinned now, and the app states what it actually needs: macOS 15 or later.
A download that finds no peers now says so. "Nothing arrived from the swarm", instead of a progress bar sitting at 0% while you work out whether to keep waiting.
The mouse pointer gets out of the way during playback on desktop.