The banner only reacted to app lifecycle, so the HEVC decoder and HLS
stream kept running behind covered routes and inactive tabs. It now
follows TickerMode: the Navigator already disables it for covered
routes, and the shell disables it for non-current tabs (which also
mutes stray animations on kept-alive pages).
Add a MotionHeaderBanner (video_player) that plays a looping muted HLS header video with a static image fallback for artist, album, and playlist screens. The Go backend now exposes header_video, header_image, and audio_traits from extensions. Album/playlist headers show the release year and Dolby Atmos / Lossless badges inline, full date and song count in a footer, a centered square cover when no video is present, and a full-bleed video when one is.