refactor(dedup): route inline shuffle + union-dedupe through existing utils (Phase L, part 2) (#691)

Findings 3 + 4 of the dedup audit — replace hand-rolled copies with the
utils that already exist:

- shuffleArray (utils/playback/shuffleArray.ts): BecauseYouLikeRail's
  local shuffle<T>, plus the inline Fisher-Yates loops in RandomAlbums,
  AlbumDetail and Home.
- dedupeById (utils/dedupeById.ts): the identical seen-Set/filter
  union-dedupe block in the fetchByGenres of Albums, NewReleases and
  RandomAlbums.

The extracted utils are character-identical to the inline loops, so no
behaviour change. RandomMix's biased `.sort(() => Math.random() - 0.5)`
is intentionally left alone — swapping it would change behaviour.

src/components/BecauseYouLikeRail.tsx

@@ -3,6 +3,7 @@ import { getArtist, getArtistInfo } from '../api/subsonicArtists';
 import { getAlbum } from '../api/subsonicLibrary';
 import type { SubsonicAlbum } from '../api/subsonicTypes';
 import { songToTrack } from '../utils/playback/songToTrack';
+import { shuffleArray } from '../utils/playback/shuffleArray';
 import React, { memo, useEffect, useMemo, useRef, useState } from 'react';
 import { useNavigate } from 'react-router-dom';
 import { useTranslation } from 'react-i18next';
@@ -39,15 +40,6 @@ const SHOW_COUNT = 3;
 const PICKS_HISTORY_SIZE = 30;
 const COVER_SIZE = 300;
 
-function shuffle<T>(arr: T[]): T[] {
-  const out = arr.slice();
-  for (let i = out.length - 1; i > 0; i--) {
-    const j = Math.floor(Math.random() * (i + 1));
-    [out[i], out[j]] = [out[j], out[i]];
-  }
-  return out;
-}
-
 interface Anchor {
   id: string;
   name: string;
@@ -162,7 +154,7 @@ export default function BecauseYouLikeRail({
     const recentAnchors = new Set(anchorHistory.slice(-cooldown));
     const eligibleRaw = pool.filter(a => !recentAnchors.has(a.id));
     const eligible = eligibleRaw.length > 0 ? eligibleRaw : pool.slice();
-    const candidates = shuffle(eligible);
+    const candidates = shuffleArray(eligible);
     const recentPicks = new Set(picksHistory);
 
     (async () => {
@@ -182,7 +174,7 @@ export default function BecauseYouLikeRail({
           const similar = (info.similarArtist ?? []).filter(s => s.id);
           if (similar.length === 0) continue;
 
-          const sampled = shuffle(similar).slice(0, SIMILAR_PICK);
+          const sampled = shuffleArray(similar).slice(0, SIMILAR_PICK);
           const results = await Promise.all(
             sampled.map(s => getArtist(s.id).catch(() => null))
           );