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/store/playlistLayoutStore.ts

@@ -0,0 +1,68 @@
+import { create } from 'zustand';
+import { persist } from 'zustand/middleware';
+
+export type PlaylistLayoutItemId =
+  | 'addSongs'
+  | 'importCsv'
+  | 'downloadZip'
+  | 'offlineCache'
+  | 'suggestions';
+
+export interface PlaylistLayoutItemConfig {
+  id: PlaylistLayoutItemId;
+  visible: boolean;
+}
+
+export const DEFAULT_PLAYLIST_LAYOUT_ITEMS: PlaylistLayoutItemConfig[] = [
+  { id: 'addSongs',     visible: true },
+  { id: 'importCsv',    visible: true },
+  { id: 'downloadZip',  visible: true },
+  { id: 'offlineCache', visible: true },
+  { id: 'suggestions',  visible: true },
+];
+
+interface PlaylistLayoutStore {
+  items: PlaylistLayoutItemConfig[];
+  setItems: (items: PlaylistLayoutItemConfig[]) => void;
+  toggleItem: (id: PlaylistLayoutItemId) => void;
+  reset: () => void;
+}
+
+export const usePlaylistLayoutStore = create<PlaylistLayoutStore>()(
+  persist(
+    (set) => ({
+      items: DEFAULT_PLAYLIST_LAYOUT_ITEMS,
+
+      setItems: (items) => set({ items }),
+
+      toggleItem: (id) => set((s) => ({
+        items: s.items.map(it => it.id === id ? { ...it, visible: !it.visible } : it),
+      })),
+
+      reset: () => set({ items: DEFAULT_PLAYLIST_LAYOUT_ITEMS }),
+    }),
+    {
+      name: 'psysonic_playlist_layout',
+      onRehydrateStorage: () => (state) => {
+        if (!state) return;
+        const knownIds = new Set(DEFAULT_PLAYLIST_LAYOUT_ITEMS.map(i => i.id));
+        const safe = (state.items ?? [])
+          .filter((i): i is PlaylistLayoutItemConfig =>
+            i != null && typeof i.id === 'string' && knownIds.has(i.id as PlaylistLayoutItemId));
+        const seen = new Set(safe.map(i => i.id));
+        const missing = DEFAULT_PLAYLIST_LAYOUT_ITEMS.filter(i => !seen.has(i.id));
+        state.items = missing.length > 0 ? [...safe, ...missing] : safe;
+      },
+    }
+  )
+);
+
+export function isPlaylistLayoutCustomized(items: PlaylistLayoutItemConfig[]): boolean {
+  if (items.length !== DEFAULT_PLAYLIST_LAYOUT_ITEMS.length) return true;
+  for (let i = 0; i < items.length; i++) {
+    const cur = items[i];
+    const def = DEFAULT_PLAYLIST_LAYOUT_ITEMS[i];
+    if (cur.id !== def.id || cur.visible !== def.visible) return true;
+  }
+  return false;
+}