Lay the party logo over the background

Centred, spanning 60% of the screen width, on the poster's layer so the
video frame and the stills still pass in front of it. The file lives in
assets/ with the posters, so it has to be kept out of the background
rotation — it is the one image there that is never a background.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01H9v2Xoa6eoeGYpK6gp95k9

public/player/index.html

@@ -9,6 +9,10 @@
   <body>
     <div id="backgrounds"></div>
 
+    <!-- The party's logo, centred over the poster. Its src and width come from
+         the shared config, so the file can be swapped without touching this. -->
+    <img id="logo" alt="" />
+
     <!-- Frozen screenshots of the frame. A sibling, not a child, of #frameMover:
          these are positioned against the screen, not the moving frame. -->
     <div id="stills"></div>