feat(config): add configurable default shutdown delay for shutdown actions

ts/actions/base-action.ts

@@ -74,7 +74,7 @@ export interface IActionConfig {
   };
 
   // Shutdown action configuration
-  /** Delay before shutdown in minutes (default: 5) */
+  /** Delay before shutdown in minutes (defaults to the config-level shutdown delay, or 5) */
   shutdownDelay?: number;
   /** Only execute shutdown on threshold violation, not power status changes */
   onlyOnThresholdViolation?: boolean;

ts/actions/shutdown-action.ts

@@ -124,7 +124,7 @@ export class ShutdownAction extends Action {
       return;
     }
 
-    const shutdownDelay = this.config.shutdownDelay || SHUTDOWN.DEFAULT_DELAY_MINUTES;
+    const shutdownDelay = this.config.shutdownDelay ?? SHUTDOWN.DEFAULT_DELAY_MINUTES;
 
     logger.log('');
     logger.logBoxTitle('Initiating System Shutdown', UI.WIDE_BOX_WIDTH, 'error');