feat(artist-detail): user-configurable visibility and order of page sections (closes #252) (#254)

Per bcorporaal's request in #252: album-oriented listeners want a
cleaner artist page focused on the album grid, with the freedom to
reorder/hide bio, top tracks, and similar artists.

Five sections are now reorder- and toggle-able from Settings →
Personalisation → "Artist page sections": Bio, Top tracks, Similar
artists, Albums, Also featured on. The fixed header block (artist
photo, name, action buttons) stays at the top.

Implementation reuses the existing sidebar customizer pattern:

- new `src/store/artistLayoutStore.ts` modelled on `sidebarStore.ts`
  with the same persist + onRehydrateStorage migration so future-added
  sections don't silently disappear from existing users' configs.
- `ArtistDetail.tsx` render block refactored from a flat sequence of
  conditional JSX into a `renderableSectionIds.map()` driven by the
  store. The "first rendered section gets marginTop: 0" rule now
  works regardless of the configured order — both hidden-by-toggle
  and empty-data sections are filtered before the layout decides
  what's first.
- `ArtistLayoutCustomizer` component in Settings, lifted from
  `LyricsSourcesCustomizer` (drag via `useDragSource` + `psy-drop`
  event, per-row toggle, reset button).
- 7 new i18n keys per locale across all 8 languages.

The store hook MUST stay above the loading / !artist early returns —
otherwise React's hook call order mismatches between renders and the
component fails silently. Lesson learned during the refactor.

Co-authored-by: Psychotoxical <dev@psysonic.app>
Co-authored-by: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/store/artistLayoutStore.ts

@@ -0,0 +1,58 @@
+import { create } from 'zustand';
+import { persist } from 'zustand/middleware';
+
+export type ArtistSectionId = 'bio' | 'topTracks' | 'similar' | 'albums' | 'featured';
+
+export interface ArtistSectionConfig {
+  id: ArtistSectionId;
+  visible: boolean;
+}
+
+/**
+ * Default order matches the historical layout of `pages/ArtistDetail.tsx` so
+ * existing users see no change until they explicitly customise it.
+ */
+export const DEFAULT_ARTIST_SECTIONS: ArtistSectionConfig[] = [
+  { id: 'bio',       visible: true },
+  { id: 'topTracks', visible: true },
+  { id: 'similar',   visible: true },
+  { id: 'albums',    visible: true },
+  { id: 'featured',  visible: true },
+];
+
+interface ArtistLayoutStore {
+  sections: ArtistSectionConfig[];
+  setSections: (sections: ArtistSectionConfig[]) => void;
+  toggleSection: (id: ArtistSectionId) => void;
+  reset: () => void;
+}
+
+export const useArtistLayoutStore = create<ArtistLayoutStore>()(
+  persist(
+    (set) => ({
+      sections: DEFAULT_ARTIST_SECTIONS,
+
+      setSections: (sections) => set({ sections }),
+
+      toggleSection: (id) => set((s) => ({
+        sections: s.sections.map(sec => sec.id === id ? { ...sec, visible: !sec.visible } : sec),
+      })),
+
+      reset: () => set({ sections: DEFAULT_ARTIST_SECTIONS }),
+    }),
+    {
+      name: 'psysonic_artist_layout',
+      onRehydrateStorage: () => (state) => {
+        if (!state) return;
+        // Sanitize: drop null/corrupt entries, append any new sections that
+        // were added in a later release so they don't silently disappear.
+        const knownIds = new Set(DEFAULT_ARTIST_SECTIONS.map(s => s.id));
+        const safe = (state.sections ?? [])
+          .filter((s): s is ArtistSectionConfig => s != null && typeof s.id === 'string' && knownIds.has(s.id as ArtistSectionId));
+        const seen = new Set(safe.map(s => s.id));
+        const missing = DEFAULT_ARTIST_SECTIONS.filter(s => !seen.has(s.id));
+        state.sections = missing.length > 0 ? [...safe, ...missing] : safe;
+      },
+    }
+  )
+);