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/api/subsonic.ts

@@ -169,6 +169,15 @@ export async function getRandomSongs(size = 50, genre?: string, timeout = 15000)
   return data.randomSongs?.song ?? [];
 }
 
+export async function getSong(id: string): Promise<SubsonicSong | null> {
+  try {
+    const data = await api<{ song: SubsonicSong }>('getSong.view', { id });
+    return data.song ?? null;
+  } catch {
+    return null;
+  }
+}
+
 export async function getAlbum(id: string): Promise<{ album: SubsonicAlbum; songs: SubsonicSong[] }> {
   const data = await api<{ album: SubsonicAlbum & { song: SubsonicSong[] } }>('getAlbum.view', { id });
   const { song, ...album } = data.album;