Alert

// ── Alert ──
pub fn buildAlert(scope: *ui.Scope, cx: *ui.Cx) anyerror!*ui.Node {
    const a = cx.allocator;
    const c = try col(cx, 12);
    // 全 4 变体，且都带 closable（× 关闭按钮）
    try c.appendChild(a, try W.Alert(.{ .variant = .info, .title = "Info", .message = "Informational message.", .closable = true }).mount(scope, cx));
    try c.appendChild(a, try W.Alert(.{ .variant = .success, .title = "Success", .message = "It worked.", .closable = true }).mount(scope, cx));
    try c.appendChild(a, try W.Alert(.{ .variant = .warning, .title = "Warning", .message = "Be careful.", .closable = true }).mount(scope, cx));
    try c.appendChild(a, try W.Alert(.{ .variant = .@"error", .title = "Error", .message = "Something broke.", .closable = true }).mount(scope, cx));
    // 无标题（仅 message）
    try c.appendChild(a, try W.Alert(.{ .variant = .info, .message = "Title-less alert with just a message." }).mount(scope, cx));
    return c;
}