feat(cli): add action management commands

Added comprehensive action management:

Commands:
- nupst action add <ups-id> - Add a new action to a UPS interactively
- nupst action remove <ups-id> <index> - Remove an action by index
- nupst action list [ups-id] - List all actions (optionally for specific UPS)

Features:
- Interactive prompts for action configuration
- Battery and runtime threshold configuration
- Trigger mode selection (onlyPowerChanges, onlyThresholds, powerChangesAndThresholds, anyChange)
- Shutdown delay configuration
- Table-based display of actions with indices
- Support for managing actions across multiple UPS devices

Implementation:
- Created ActionHandler class in ts/cli/action-handler.ts
- Integrated with existing CLI infrastructure
- Added to nupst.ts, cli.ts, and help system
- Proper TypeScript typing throughout

Closes the gap where users had to manually edit config.json to manage actions.

ts/nupst.ts

@@ -6,6 +6,7 @@ import { logger } from './logger.ts';
 import { UpsHandler } from './cli/ups-handler.ts';
 import { GroupHandler } from './cli/group-handler.ts';
 import { ServiceHandler } from './cli/service-handler.ts';
+import { ActionHandler } from './cli/action-handler.ts';
 import * as https from 'node:https';
 
 /**
@@ -19,6 +20,7 @@ export class Nupst {
   private readonly upsHandler: UpsHandler;
   private readonly groupHandler: GroupHandler;
   private readonly serviceHandler: ServiceHandler;
+  private readonly actionHandler: ActionHandler;
   private updateAvailable: boolean = false;
   private latestVersion: string = '';
 
@@ -36,6 +38,7 @@ export class Nupst {
     this.upsHandler = new UpsHandler(this);
     this.groupHandler = new GroupHandler(this);
     this.serviceHandler = new ServiceHandler(this);
+    this.actionHandler = new ActionHandler(this);
   }
 
   /**
@@ -80,6 +83,13 @@ export class Nupst {
     return this.serviceHandler;
   }
 
+  /**
+   * Get the Action handler for action management
+   */
+  public getActionHandler(): ActionHandler {
+    return this.actionHandler;
+  }
+
   /**
    * Get the current version of NUPST
    * @returns The current version string