Invoke systemctl via PATH instead of /usr/bin

The absolute path assumes an FHS layout and fails on distributions that
place systemctl elsewhere, such as NixOS.

Cargo.lock

@@ -575,7 +575,7 @@ dependencies = [
 
 [[package]]
 name = "moonlock"
-version = "0.6.20"
+version = "0.6.21"
 dependencies = [
  "gdk-pixbuf",
  "gdk4",

Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "moonlock"
-version = "0.6.20"
+version = "0.6.21"
 edition = "2024"
 description = "A secure Wayland lockscreen with GTK4, PAM and fingerprint support"
 license = "MIT"

src/power.rs

@@ -34,8 +34,8 @@ fn run_command(action: &'static str, program: &str, args: &[&str]) -> Result<(),
     Ok(())
 }
 
-pub fn reboot() -> Result<(), PowerError> { run_command("reboot", "/usr/bin/systemctl", &["--no-ask-password", "reboot"]) }
+pub fn reboot() -> Result<(), PowerError> { run_command("reboot", "systemctl", &["--no-ask-password", "reboot"]) }
-pub fn shutdown() -> Result<(), PowerError> { run_command("shutdown", "/usr/bin/systemctl", &["--no-ask-password", "poweroff"]) }
+pub fn shutdown() -> Result<(), PowerError> { run_command("shutdown", "systemctl", &["--no-ask-password", "poweroff"]) }
 
 #[cfg(test)]
 mod tests {