feat: add laptop/display brightness modulation

programs/src/desktop/panel.cpp

@@ -173,6 +173,17 @@ void gui::desktop_draw_panel(DesktopState* ds) {
     int icon_y = (PANEL_HEIGHT - 16) / 2;
     int next_icon_x = vol_icon_x - 16 - 10;
 
+    // Brightness sits next to the speaker: the two slider controls together.
+    if (ds->brightness_present) {
+        ds->brightness_icon_rect = {next_icon_x, icon_y, 16, 16};
+        next_icon_x -= 16 + 10;
+        if (ds->icon_brightness.pixels)
+            fb.blit_alpha(ds->brightness_icon_rect.x, icon_y, ds->icon_brightness.width,
+                          ds->icon_brightness.height, ds->icon_brightness.pixels);
+    } else {
+        ds->brightness_icon_rect = {0, 0, 0, 0};
+    }
+
     if (ds->eth_present) {
         ds->net_icon_rect = {next_icon_x, icon_y, 16, 16};
         next_icon_x -= 16 + 10;