Rewrite the README so it leads with what JTube TV is and who it's for, refresh
the feature list and screenshot captions to match the current UI (three Home
rows, Back opens the sidebar, Subscribe on the channel page), and add the
official PeerTube logo next to the name. Screenshot images are refreshed in a
follow-up.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
