redbear-sessiond: emit SeatRemoved on shutdown

Completes the SeatNew/SeatRemoved pair from the prior commit. The
emit_seat_removed public method was added but not wired to any shutdown
path; this commit hooks it into wait_for_shutdown's return path so
subscribers (e.g. SDDM's LogindSeatManager) observe seat departure
before the D-Bus connection drops. SEAT_PATH is reused from main.rs's
existing constant rather than introducing a new placeholder string.

local/recipes/system/redbear-sessiond/source/src/main.rs

@@ -205,6 +205,23 @@ async fn run_daemon() -> Result<(), Box<dyn Error>> {
                 control::start_control_socket(runtime.clone(), shutdown_tx.clone());
                 tokio::spawn(acpi_watcher::watch_and_emit(connection.clone(), runtime.clone()));
                 wait_for_shutdown(shutdown_rx).await?;
+                // Order: emit before drop so subscribers see SeatRemoved before the bus connection closes.
+                let seat_id = match runtime.read() {
+                    Ok(runtime) => runtime.seat_id.clone(),
+                    Err(_) => String::from("seat0"),
+                };
+                let seat_path =
+                    match zbus::zvariant::OwnedObjectPath::try_from(SEAT_PATH.to_owned()) {
+                        Ok(p) => p,
+                        Err(_) => {
+                            eprintln!(
+                                "redbear-sessiond: SEAT_PATH constant is not a valid D-Bus path; skipping SeatRemoved"
+                            );
+                            drop(connection);
+                            return Ok(());
+                        }
+                    };
+                manager_ref.emit_seat_removed(&seat_id, &seat_path).await;
                 drop(connection);
                 return Ok(());
             }