feat: v1.8.0 — new themes, queue toolbar, lightbox, i18n (fr/nl)

Themes:
- Add Poison (phosphor green on charcoal), Nucleo (warm brass light), Classic Winamp (LCD glow, Winamp yellow/orange) themes
- Overhaul Psychowave — refined deep violet, no longer WIP
- Reorganise ThemePicker into groups: Catppuccin, Nord, Retro, Tokyo Night, Psysonic Themes
- Add --volume-accent CSS var for per-theme volume slider colour override

Queue:
- Full toolbar redesign with centred round buttons (Shuffle/Save/Load/Clear/Gapless/Crossfade)
- Crossfade popover with 1–10 s range slider, right-aligned to avoid viewport overflow
- Queue header: title + count + duration inline in accent colour, close button removed
- Tech info (codec/bitrate) as frosted-glass overlay badge on cover art

UI:
- CoverLightbox shared component for album cover (AlbumHeader) and artist avatar (ArtistDetail)
- NowPlayingDropdown: separate spinning/loading state — button always clickable, icon spins 600 ms min
- Settings: "Experimental" badge on Crossfade and Gapless toggles
- Help page: 2-column grid layout, new Crossfade & Gapless Q&A entry, updated theme/language entries

i18n:
- Full French (fr) and Dutch (nl) translations across all namespaces
- Language selector sorted alphabetically (nl, en, fr, de)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/store/authStore.ts

@@ -37,6 +37,7 @@ interface AuthState {
   isLoggedIn: boolean;
   isConnecting: boolean;
   connectionError: string | null;
+  lastfmSessionError: boolean;
 
   // Actions
   addServer: (profile: Omit<ServerProfile, 'id'>) => string;
@@ -49,6 +50,7 @@ interface AuthState {
   setLastfm: (apiKey: string, apiSecret: string, sessionKey: string, username: string) => void;
   connectLastfm: (sessionKey: string, username: string) => void;
   disconnectLastfm: () => void;
+  setLastfmSessionError: (v: boolean) => void;
   setMinimizeToTray: (v: boolean) => void;
   setScrobblingEnabled: (v: boolean) => void;
   setMaxCacheMb: (v: number) => void;
@@ -94,6 +96,7 @@ export const useAuthStore = create<AuthState>()(
       isLoggedIn: false,
       isConnecting: false,
       connectionError: null,
+      lastfmSessionError: false,
 
       addServer: (profile) => {
         const id = generateId();
@@ -132,7 +135,9 @@ export const useAuthStore = create<AuthState>()(
         set({ lastfmSessionKey: sessionKey, lastfmUsername: username }),
 
       disconnectLastfm: () =>
-        set({ lastfmSessionKey: '', lastfmUsername: '' }),
+        set({ lastfmSessionKey: '', lastfmUsername: '', lastfmSessionError: false }),
+
+      setLastfmSessionError: (v) => set({ lastfmSessionError: v }),
 
       setMinimizeToTray: (v) => set({ minimizeToTray: v }),
       setScrobblingEnabled: (v) => set({ scrobblingEnabled: v }),