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

server/state.js

@@ -6,7 +6,13 @@ import { dirname, join } from 'node:path';
 import { fileURLToPath } from 'node:url';
 import { randomUUID } from 'node:crypto';
 
-import { DEFAULT_BACKGROUND, BACKGROUNDS } from '../config.js';
+import {
+  DEFAULT_BACKGROUND,
+  BACKGROUNDS,
+  DEFAULT_ANIMATION,
+  ANIMATIONS,
+  AUTO_ANIMATION,
+} from '../config.js';
 
 const ROOT = join(dirname(fileURLToPath(import.meta.url)), '..');
 const STORE_PATH = join(ROOT, 'queue.json');
@@ -15,12 +21,18 @@ const state = {
   items: [],
   currentId: null,
   background: DEFAULT_BACKGROUND,
+  animation: DEFAULT_ANIMATION,
 };
 
 export function getState() {
   return state;
 }
 
+/** Is this a name the player can be pinned to (or the auto cycle)? */
+export function isAnimation(key) {
+  return key === AUTO_ANIMATION || key in ANIMATIONS;
+}
+
 export function load() {
   try {
     const saved = JSON.parse(readFileSync(STORE_PATH, 'utf8'));
@@ -35,6 +47,7 @@ export function load() {
         }));
     }
     if (saved.background in BACKGROUNDS) state.background = saved.background;
+    if (isAnimation(saved.animation)) state.animation = saved.animation;
     // Resume at the item that was playing, otherwise at the top of the list.
     state.currentId = state.items.some((i) => i.id === saved.currentId)
       ? saved.currentId
@@ -52,7 +65,12 @@ export function load() {
  */
 export function save() {
   const payload = JSON.stringify(
-    { items: state.items, currentId: state.currentId, background: state.background },
+    {
+      items: state.items,
+      currentId: state.currentId,
+      background: state.background,
+      animation: state.animation,
+    },
     null,
     2,
   );