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/components/AlbumHeader.tsx

@@ -1,8 +1,9 @@
-import React from 'react';
+import React, { useState } from 'react';
 import { useNavigate } from 'react-router-dom';
 import { Play, Star, ExternalLink, X, ChevronLeft, Download, ListPlus, Info } from 'lucide-react';
-import { SubsonicSong } from '../api/subsonic';
+import { SubsonicSong, buildCoverArtUrl } from '../api/subsonic';
 import CachedImage from './CachedImage';
+import CoverLightbox from './CoverLightbox';
 import { useTranslation } from 'react-i18next';
 
 function formatDuration(seconds: number): string {
@@ -49,6 +50,7 @@ function BioModal({ bio, onClose }: { bio: string; onClose: () => void }) {
   );
 }
 
+
 interface AlbumInfo {
   id: string;
   name: string;
@@ -97,6 +99,7 @@ export default function AlbumHeader({
 }: AlbumHeaderProps) {
   const { t } = useTranslation();
   const navigate = useNavigate();
+  const [lightboxOpen, setLightboxOpen] = useState(false);
 
   const totalDuration = songs.reduce((acc, s) => acc + s.duration, 0);
   const totalSize = songs.reduce((acc, s) => acc + (s.size ?? 0), 0);
@@ -104,6 +107,13 @@ export default function AlbumHeader({
   return (
     <>
       {bioOpen && bio && <BioModal bio={bio} onClose={onCloseBio} />}
+      {lightboxOpen && info.coverArt && (
+        <CoverLightbox
+          src={buildCoverArtUrl(info.coverArt, 2000)}
+          alt={`${info.name} Cover`}
+          onClose={() => setLightboxOpen(false)}
+        />
+      )}
 
       <div className="album-detail-header">
         {resolvedCoverUrl && (
@@ -121,7 +131,14 @@ export default function AlbumHeader({
           </button>
           <div className="album-detail-hero">
             {coverUrl ? (
-              <CachedImage className="album-detail-cover" src={coverUrl} cacheKey={coverKey} alt={`${info.name} Cover`} />
+              <button
+                className="album-detail-cover-btn"
+                onClick={() => setLightboxOpen(true)}
+                data-tooltip="Vergrößern"
+                aria-label={`${info.name} Cover vergrößern`}
+              >
+                <CachedImage className="album-detail-cover" src={coverUrl} cacheKey={coverKey} alt={`${info.name} Cover`} />
+              </button>
             ) : (
               <div className="album-detail-cover album-cover-placeholder">♪</div>
             )}