feat: 10-band EQ, connection indicator, new icon (v1.5.0)

### 10-Band Graphic Equalizer
- Full EQ in Rust audio engine via EqSource<S> biquad peak filters
- 10 built-in presets + custom preset save/delete
- EqSource::try_seek() implemented — also fixes waveform seek which broke
  silently when EQ was introduced (rodio returned SeekError::NotSupported)
- EQ state persisted in localStorage, synced to Rust on startup

### Connection Indicator
- LED in header (green/red/pulsing) with server name and LAN/WAN label
- Offline overlay with retry button when server is unreachable
- useConnectionStatus hook

### New App Icon
- New logo (logo-psysonic.png) applied across Login, Sidebar, Settings,
  README and all Tauri platform icons (Windows, macOS, Linux, Android, iOS)

### Now Playing Page
- New /now-playing route added

### Fixes
- WaveformSeek: mousemove/mouseup on window to fix drag outside canvas

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

src/components/OfflineOverlay.tsx

@@ -0,0 +1,32 @@
+import { useTranslation } from 'react-i18next';
+import { WifiOff, RefreshCw } from 'lucide-react';
+
+interface Props {
+  serverName: string;
+  onRetry: () => void;
+  isChecking: boolean;
+}
+
+export default function OfflineOverlay({ serverName, onRetry, isChecking }: Props) {
+  const { t } = useTranslation();
+
+  return (
+    <div className="offline-overlay">
+      <div className="offline-overlay-card">
+        <WifiOff size={48} className="offline-icon" />
+        <h2 className="offline-title">{t('connection.offlineTitle')}</h2>
+        <p className="offline-subtitle">
+          {t('connection.offlineSubtitle', { server: serverName })}
+        </p>
+        <button
+          className="btn btn-primary offline-retry"
+          onClick={onRetry}
+          disabled={isChecking}
+        >
+          <RefreshCw size={16} className={isChecking ? 'spin' : ''} />
+          {isChecking ? t('connection.checking') : t('connection.retry')}
+        </button>
+      </div>
+    </div>
+  );
+}