feat(settings): global Advanced Mode toggle + playlist page layout (#556) (#720)

Adds a per-element visibility toggle for the playlist detail page (Add
Songs, Import CSV, Download ZIP, Cache Offline, Suggestions) and reworks
the way uncommon options are surfaced: instead of a per-tab collapsible
group, a global "Advanced" toggle in the Settings header reveals all
`advanced` sub-sections across every tab and marks each one with a small
badge. Sets the pattern up so any future advanced option lives in its
natural tab, gated by the same switch.

- New `advancedSettingsEnabled` boolean on `authStore`
  (UiAppearance slice, persisted with the rest of the store).
- `SettingsSubSection` gains an `advanced?: boolean` prop. Hidden when
  the toggle is off; renders an "Advanced" pill in the header when on.
- Settings header gets a Toggle-Switch next to the search lupe.
- `PersonalisationTab` flattens — Sidebar + Home stay always visible;
  Artist sections, Queue Toolbar, and the new Playlist layout get
  `advanced` and disappear by default. `PersonalisationAdvancedGroup`
  component + CSS removed.
- New `playlistLayoutStore` (Zustand + persist, items[{id,visible}] +
  rehydrate sanitize) following the queueToolbarStore pattern.
- `PlaylistHero` and `PlaylistSuggestions` gate the four toolbar buttons
  and the suggestions rail on the store directly.
- One-time migration in MainApp on mount: if the user had opened the
  old per-tab Advanced group (`psysonic_personalisation_advanced_open
  === 'true'`) OR already customised any of the three sub-sections,
  Advanced Mode auto-enables on first launch. Idempotent via a
  localStorage flag; legacy key removed afterwards.
- New i18n keys `settings.advancedMode`, `settings.advancedModeTooltip`,
  `settings.advancedBadge`, `settings.playlistLayout*` in all 9 locales.

Reuses kveld9's design from PR #556; not merged because the locale split
landed afterwards. Credited under the existing kveld9 entry in
settingsCredits.ts.

Co-authored-by: Kveld. <kveld912@proton.me>

src/locales/de/settings.ts

@@ -270,6 +270,12 @@ export const settings = {
   artistLayoutSimilar: 'Ähnliche Künstler*innen',
   artistLayoutAlbums: 'Alben',
   artistLayoutFeatured: 'Auch enthalten auf',
+  playlistLayoutTitle: 'Playlist-Seitenlayout',
+  playlistLayoutDesc: 'Einzelne Elemente auf der Playlist-Seite ein- oder ausblenden.',
+  playlistLayoutReset: 'Zurücksetzen',
+  advancedMode: 'Erweitert',
+  advancedModeTooltip: 'Erweiterte Optionen in allen Settings-Tabs anzeigen. Community-Beiträge, die nicht zwingend der Design-Philosophie der Maintainer von Psysonic entsprechen.',
+  advancedBadge: 'Erweitert',
   sidebarDrag: 'Ziehen zum Umsortieren',
   sidebarFixed: 'Immer sichtbar',
   randomNavSplitTitle: 'Mix-Navigation aufteilen',