fix(brightness): refresh sysfs cache on hotplug (#1674)

* fix(brightness): refresh sysfs cache on hotplug

The SysfsBackend used a cache that was never refreshed on display hot plug, causing new backlight devices to not appear in IPC until restart.

This adds Rescan() to SysfsBackend and calls it in Manager.Rescan(), matching the behavior of DDCBackend.

Fixes: hotplugged external monitor brightness control via IPC

* make fmt

---------

Co-authored-by: bbedward <[email protected]>

core/internal/server/brightness/manager.go

@@ -96,6 +96,12 @@ func (m *Manager) Rescan() {
 		}
 	}
 
+	if m.sysfsReady && m.sysfsBackend != nil {
+		if err := m.sysfsBackend.Rescan(); err != nil {
+			log.Debugf("Sysfs rescan failed: %v", err)
+		}
+	}
+
 	m.updateState()
 }
 

core/internal/server/brightness/sysfs.go

@@ -101,6 +101,10 @@ func shouldSuppressDevice(name string) bool {
 	return false
 }
 
+func (b *SysfsBackend) Rescan() error {
+	return b.scanDevices()
+}
+
 func (b *SysfsBackend) GetDevices() ([]Device, error) {
 	devices := make([]Device, 0)