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/LastfmIndicator.tsx

@@ -0,0 +1,39 @@
+import { useNavigate } from 'react-router-dom';
+import { useTranslation } from 'react-i18next';
+import { useAuthStore } from '../store/authStore';
+import LastfmIcon from './LastfmIcon';
+
+export default function LastfmIndicator() {
+  const { t } = useTranslation();
+  const navigate = useNavigate();
+  const { lastfmSessionKey, lastfmUsername, lastfmSessionError } = useAuthStore();
+
+  if (!lastfmSessionKey) return null;
+
+  const tooltip = lastfmSessionError
+    ? t('connection.lastfmSessionInvalid')
+    : t('connection.lastfmConnected', { user: lastfmUsername });
+
+  return (
+    <div
+      className="connection-indicator"
+      style={{ cursor: 'pointer' }}
+      onClick={() => navigate('/settings', { state: { tab: 'server' } })}
+      data-tooltip={tooltip}
+      data-tooltip-pos="bottom"
+    >
+      <div
+        className={`connection-led connection-led--${lastfmSessionError ? 'disconnected' : 'connected'}`}
+      />
+      <div className="connection-meta">
+        <span className="connection-type" style={{ display: 'flex', alignItems: 'center', gap: '4px' }}>
+          <LastfmIcon size={11} />
+          Last.fm
+        </span>
+        <span className="connection-server">
+          {lastfmSessionError ? t('connection.lastfmSessionInvalid').split(' —')[0] : `@${lastfmUsername}`}
+        </span>
+      </div>
+    </div>
+  );
+}