Allow dead_code on Error::Power variant for future use

Mirrors the existing pattern on Error::Socket. The variant is reserved
for making power sysfs/D-Bus failures hard errors (tampering detection)
instead of the current graceful degradation.

Author: AcidDemon

src/error.rs

@@ -13,6 +13,7 @@ pub enum Error {
     /// SD card enumeration failed.
     SdCard(String),
     /// Power supply monitoring failed.
+    #[allow(dead_code)]
     Power(String),
     /// Kill sequence encountered an error.
     Kill(String),