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/App.tsx

@@ -32,6 +32,7 @@ import ContextMenu from './components/ContextMenu';
 import DownloadFolderModal from './components/DownloadFolderModal';
 import TooltipPortal from './components/TooltipPortal';
 import ConnectionIndicator from './components/ConnectionIndicator';
+import LastfmIndicator from './components/LastfmIndicator';
 import OfflineOverlay from './components/OfflineOverlay';
 import { useConnectionStatus } from './hooks/useConnectionStatus';
 import { useAuthStore } from './store/authStore';
@@ -140,6 +141,7 @@ function AppShell() {
           <LiveSearch />
           <div className="spacer" />
           <ConnectionIndicator status={connStatus} isLan={isLan} serverName={serverName} />
+          <LastfmIndicator />
           <NowPlayingDropdown />
           <button
             className="collapse-btn"