feat: Allow self-service deactivation to be disabled

src/api/client/account/mod.rs

@@ -285,6 +285,13 @@ pub(crate) async fn deactivate_route(
 
 	let sender_user = identity.expect_sender_user()?;
 
+	if !services.config.allow_deactivation {
+		return Err!(Request(Unauthorized(
+			"You may not deactivate your own account. Contact your server's administrator for \
+			 assistance."
+		)));
+	}
+
 	// Prompt the user to confirm with their password using UIAA
 	let _ = services
 		.uiaa