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-tauri/src/lib.rs

@@ -25,6 +25,7 @@ pub fn run() {
 
     tauri::Builder::default()
         .manage(audio_engine)
+        .plugin(tauri_plugin_window_state::Builder::default().build())
         .plugin(tauri_plugin_shell::init())
         .plugin(tauri_plugin_notification::init())
         .plugin(tauri_plugin_global_shortcut::Builder::new().build())
@@ -124,6 +125,7 @@ pub fn run() {
             audio::audio_stop,
             audio::audio_seek,
             audio::audio_set_volume,
+            audio::audio_set_eq,
         ])
         .run(tauri::generate_context!())
         .expect("error while running Psysonic");