feat(game): play confetti for finished games

src/utils/confetti.js

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+const FINISHED = ['FINISHED', 'COMPLETED'];
+
+/**
+ * Every achievement unlocked. Only while the stats are visible: Core can still send the old unlock count after they turn private.
+ */
+export const allAchievementsUnlocked = (game) => game.hasAchievements && game.statsVisible
+    && game.achievementsTotal > 0 && game.achievementsUnlocked >= game.achievementsTotal;
+
+/**
+ * 0: not finished, 1: finished, 2: finished and every achievement unlocked.
+ */
+export const celebrationLevel = (game) => {
+    if (!FINISHED.includes(game.status)) return 0;
+    return allAchievementsUnlocked(game) ? 2 : 1;
+};
+
+/**
+ * The confetti to play when the page shows this game: on opening a finished game, and when the level rises on the
+ * same page (e.g. the user sets FINISHED). A reload of the same game plays nothing.
+ *
+ * @param before {appid, level} of the game shown before, null on opening the page
+ * @returns 'small', 'big' or null
+ */
+export const celebrationFor = (before, game) => {
+    const level = celebrationLevel(game);
+    const from = before?.appid === game.appid ? before.level : 0;
+    if (level <= from) return null;
+    return level === 2 ? 'big' : 'small';
+};