fix(daemon): call shutdown directly rather than binding a unit value

Clippy's let_unit_value, caught in review of the previous commit: shutdown()
returns (), so the let-binding was noise.

Co-Authored-By: Claude Code <noreply@anthropic.com>

desktop/daemon/src/main.rs

@@ -125,7 +125,7 @@ fn main() -> ExitCode {
         };
         println!("owning the D-Bus name; entering the event loop");
         run_loop(&rx, &schedules, &usage, &context, blocker_platform_linux::Enforcement::Freeze);
-        let _ = backend.shutdown();
+        backend.shutdown();
         return ExitCode::SUCCESS;
     }