Let the queue page pin the frame animation

Waiting for the shuffle bag to land on the animation you are working on makes
testing one of them tedious. The queue page now carries an Animation row next
to Background: Auto keeps the per-track cycle, any other button pins the player
to that animation until the mode changes again.

The animation names live in config.js alongside their labels, so the server can
validate them and the queue page can label its buttons; motion.js keys its
registry by the same names.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Tg15tLAuT6NrCE1ZxKVgDB

public/queue/queue.css

@@ -241,13 +241,20 @@ footer {
   border-top: 1px solid #331630;
 }
 
-#backgrounds {
+footer .switcher + .switcher {
+  margin-top: 18px;
+}
+
+#backgrounds,
+#animations {
   display: flex;
+  flex-wrap: wrap;
   gap: 8px;
   margin-top: 8px;
 }
 
-#backgrounds button {
+#backgrounds button,
+#animations button {
   font: inherit;
   padding: 8px 18px;
   border-radius: 999px;
@@ -257,7 +264,8 @@ footer {
   cursor: pointer;
 }
 
-#backgrounds button.active {
+#backgrounds button.active,
+#animations button.active {
   background: var(--accent);
   border-color: var(--accent);
   color: var(--ink);