Surface the feedpak manifest `authors` list (spec §5.4) on the highway: a credits card ("Charted by Azure") shown over the highway when a song loads, riding the count-in / a ~3s hold and dismissed when playback starts. Gated to fresh feedpak plays only (minigames, loose/archive, arrangement switches, seeks, replays excluded). Includes a 12s backstop so the overlay never lingers if playback fails to start.
Closes#628. Reviewed by Codex (3 passes, converged). Verified locally: pytest 9/9, node --test 23/23, headless-browser end-to-end.
