fix(lint): remove unnecessary async keywords from synchronous functions

- Remove async from functions that don't use await
- Change return types from Promise<void> to void for synchronous functions
- Fixes all 8 require-await lint warnings
- Reduces total lint warnings from 63 to 55

ts/systemd.ts

@@ -119,7 +119,7 @@ WantedBy=multi-user.target
    * Stop the systemd service
    * @throws Error if stop fails
    */
-  public async stop(): Promise<void> {
+  public stop(): void {
     try {
       execSync('systemctl stop nupst.service');
       logger.success('NUPST service stopped');
@@ -168,7 +168,7 @@ WantedBy=multi-user.target
    * Display the systemd service status
    * @private
    */
-  private async displayServiceStatus(): Promise<void> {
+  private displayServiceStatus(): void {
     try {
       const serviceStatus = execSync('systemctl status nupst.service').toString();
       const boxWidth = 45;
@@ -315,7 +315,7 @@ WantedBy=multi-user.target
    * Stop the service if it's running
    * @private
    */
-  private async stopService(): Promise<void> {
+  private stopService(): void {
     try {
       logger.log('Stopping NUPST service...');
       execSync('systemctl stop nupst.service');
@@ -329,7 +329,7 @@ WantedBy=multi-user.target
    * Disable the service
    * @private
    */
-  private async disableService(): Promise<void> {
+  private disableService(): void {
     try {
       logger.log('Disabling NUPST service...');
       execSync('systemctl disable nupst.service');