Replace the placeholder-content screenshots with a demo instance that
serves real CC-licensed open movies (Blender Foundation, framatube),
so the app looks like what it is: a video player with real thumbnails,
real durations and real playback.
Rewrite the README around what a user sees: what the app is for, how
the screens look and what to press. Add the logo, five screenshots
taken against a local mock PeerTube instance with placeholder content
(no private media), and a debug-only manifest that allows plain HTTP
so those mock instances work.
