feat(library): "favorites only" filter on Albums, Artists, AdvancedSearch (#466)

* feat(ui): StarFilterButton component + common i18n keys

Reusable toggle button for "favorites only" filtering. Three size
variants for different toolbar contexts:
- default: icon + label (Albums-style)
- compact: icon-only with 0.5rem padding (Artists view-mode buttons)
- small:   icon + label at 12px / 4×14 padding (AdvancedSearch tabs)

Adds common.favorites + favoritesTooltipOff/On in all 8 locales.

* feat(library): "favorites only" filter on Albums, Artists, AdvancedSearch

Client-side filter using the existing useMemo pipelines on each page.
Reads starred state from item.starred + playerStore.starredOverrides
(O(1) Map lookup, picks up live star toggles without refetch).

- Albums: toolbar button (default size) next to compilation filter.
- Artists: toolbar button (compact / icon-only) before the Images toggle.
- AdvancedSearch: toolbar button (small) next to the result-type tabs;
  filters all three result categories (artists / albums / songs) and
  updates the count badges accordingly.

Filter state is ephemeral per-page (not persisted) so users don't get
surprised by hidden items after a restart. Zero extra server calls.

* docs(contributors): credit + changelog entry for #466

src/components/StarFilterButton.tsx

@@ -0,0 +1,68 @@
+import { Star } from 'lucide-react';
+import { useTranslation } from 'react-i18next';
+
+interface Props {
+  active: boolean;
+  onChange: (next: boolean) => void;
+  /** 'default' = icon + label, regular padding (Albums toolbar).
+   *  'compact' = icon-only, 0.5rem padding (Artists view-mode buttons).
+   *  'small'   = icon + label, 4px/14px padding + 12px text (AdvancedSearch tabs). */
+  size?: 'default' | 'compact' | 'small';
+}
+
+export default function StarFilterButton({ active, onChange, size = 'default' }: Props) {
+  const { t } = useTranslation();
+  const tooltip = active ? t('common.favoritesTooltipOn') : t('common.favoritesTooltipOff');
+  const activeStyle = active ? { background: 'var(--accent)', color: 'var(--ctp-crust)' } : {};
+
+  if (size === 'compact') {
+    return (
+      <button
+        type="button"
+        className={`btn btn-surface${active ? ' btn-sort-active' : ''}`}
+        onClick={() => onChange(!active)}
+        aria-pressed={active}
+        aria-label={tooltip}
+        data-tooltip={tooltip}
+        data-tooltip-pos="bottom"
+        style={{ padding: '0.5rem', ...activeStyle }}
+      >
+        <Star size={20} fill={active ? 'currentColor' : 'none'} />
+      </button>
+    );
+  }
+
+  if (size === 'small') {
+    return (
+      <button
+        type="button"
+        className={`btn ${active ? 'btn-primary' : 'btn-surface'}`}
+        onClick={() => onChange(!active)}
+        aria-pressed={active}
+        data-tooltip={tooltip}
+        data-tooltip-pos="bottom"
+        style={{ fontSize: 12, padding: '4px 14px', display: 'inline-flex', alignItems: 'center', gap: '0.35rem' }}
+      >
+        <Star size={12} fill={active ? 'currentColor' : 'none'} />
+        {t('common.favorites')}
+      </button>
+    );
+  }
+
+  return (
+    <button
+      type="button"
+      className={`btn btn-surface${active ? ' btn-sort-active' : ''}`}
+      onClick={() => onChange(!active)}
+      aria-pressed={active}
+      data-tooltip={tooltip}
+      data-tooltip-pos="bottom"
+      style={{
+        display: 'flex', alignItems: 'center', gap: '0.4rem', ...activeStyle,
+      }}
+    >
+      <Star size={14} fill={active ? 'currentColor' : 'none'} />
+      {t('common.favorites')}
+    </button>
+  );
+}