Wire skill level and accessibility settings to UI

- Add detailed_mode to AppState, derived from skill_level setting
- Expand advanced option sections by default in Detailed mode
  (resize, convert, compress, watermark steps)
- Fix high contrast to use HighContrast GTK theme
- Add completion sound via canberra-gtk-play

pixstrip-gtk/src/steps/step_compress.rs

@@ -295,6 +295,7 @@ pub fn build_compress_page(state: &AppState) -> adw::NavigationPage {
     let advanced_expander = adw::ExpanderRow::builder()
         .title("Per-Format Quality")
         .subtitle("Fine-tune quality for each format individually")
+        .expanded(state.detailed_mode)
         .build();
 
     let jpeg_row = adw::SpinRow::builder()