feat: add laptop/display brightness modulation

programs/src/desktop/main.cpp

@@ -393,6 +393,7 @@ void gui::desktop_init(DesktopState* ds) {
     desktop_refresh_netifs(ds);
     desktop_wifi_init(ds);
     desktop_battery_init(ds);
+    desktop_brightness_init(ds);
     desktop_consent_init(ds);
 
     ds->vol_popup_open = false;
@@ -445,6 +446,7 @@ static bool desktop_has_visible_dirty_window(const DesktopState* ds) {
 
 static bool desktop_has_active_interaction(const DesktopState* ds) {
     if (ds->vol_dragging) return true;
+    if (desktop_brightness_dragging(ds)) return true;
 
     for (int i = 0; i < ds->window_count; i++) {
         const Window& win = ds->windows[i];
@@ -521,6 +523,7 @@ static bool desktop_refresh_panel_state(DesktopState* ds, uint64_t now) {
 
     if (desktop_wifi_poll(ds, now)) changed = true;
     if (desktop_battery_poll(ds, now)) changed = true;
+    if (desktop_brightness_poll(ds, now)) changed = true;
 
     // Event-driven sync: the kernel mixer bumps a serial on every state
     // change. Reading it is one cheap syscall; refresh only when the serial