fix: Display a nicer message for failed logins

This commit technically closes #41 but the issue is deeper than the
message itself. The message `unable to send message: Connection refused
(os error 111)` overrides the failed login prompt. `COSMIC greeter`
seems to be sending a stray message over the socket.

i18n/en/cosmic_greeter.ftl

@@ -5,3 +5,7 @@ restart-timeout = The system will restart automatically in {$seconds} seconds.
 shutdown = Shut down
 shutdown-now = Shut down now?
 shutdown-timeout = The system will shut down automatically in {$seconds} seconds.
+
+# Error messages
+auth-failed = You entered an invalid password.
+try-again = Please try again.

src/greeter.rs

@@ -309,11 +309,17 @@ async fn request_message(socket: Arc<UnixStream>, request: Request) -> Message {
                         }
                     },
                     Response::Error {
-                        error_type: _,
+                        error_type: error,
                         description,
                     } => {
-                        //TODO: use error_type?
-                        return Message::Error(socket, description);
+                        log::error!("{error:?} => {description}");
+                        return match error {
+                            greetd_ipc::ErrorType::AuthError => Message::Error(
+                                socket,
+                                format!("{} {}", fl!("auth-failed"), fl!("try-again")),
+                            ),
+                            greetd_ipc::ErrorType::Error => Message::Error(socket, description),
+                        };
                     }
                     Response::Success => match request {
                         Request::CreateSession { .. } => {