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/cli.ts

@@ -72,6 +72,7 @@ export class NupstCli {
     const upsHandler = this.nupst.getUpsHandler();
     const groupHandler = this.nupst.getGroupHandler();
     const serviceHandler = this.nupst.getServiceHandler();
+    const actionHandler = this.nupst.getActionHandler();
 
     // Handle service subcommands
     if (command === 'service') {
@@ -193,6 +194,38 @@ export class NupstCli {
       return;
     }
 
+    // Handle action subcommands
+    if (command === 'action') {
+      const subcommand = commandArgs[0] || 'list';
+      const subcommandArgs = commandArgs.slice(1);
+
+      switch (subcommand) {
+        case 'add': {
+          const upsId = subcommandArgs[0];
+          await actionHandler.add(upsId);
+          break;
+        }
+        case 'remove':
+        case 'rm': // Alias
+        case 'delete': { // Backward compatibility
+          const upsId = subcommandArgs[0];
+          const actionIndex = subcommandArgs[1];
+          await actionHandler.remove(upsId, actionIndex);
+          break;
+        }
+        case 'list':
+        case 'ls': { // Alias
+          const upsId = subcommandArgs[0];
+          await actionHandler.list(upsId);
+          break;
+        }
+        default:
+          this.showActionHelp();
+          break;
+      }
+      return;
+    }
+
     // Handle config subcommand
     if (command === 'config') {
       const subcommand = commandArgs[0] || 'show';
@@ -499,6 +532,7 @@ export class NupstCli {
     this.printCommand('service <subcommand>', 'Manage systemd service');
     this.printCommand('ups <subcommand>', 'Manage UPS devices');
     this.printCommand('group <subcommand>', 'Manage UPS groups');
+    this.printCommand('action <subcommand>', 'Manage UPS actions');
     this.printCommand('config [show]', 'Display current configuration');
     this.printCommand('update', 'Update NUPST from repository', theme.dim('(requires root)'));
     this.printCommand('uninstall', 'Completely remove NUPST', theme.dim('(requires root)'));
@@ -535,6 +569,13 @@ export class NupstCli {
     this.printCommand('nupst group list (or ls)', 'List all UPS groups');
     console.log('');
 
+    // Action subcommands
+    logger.log(theme.info('Action Subcommands:'));
+    this.printCommand('nupst action add <ups-id>', 'Add a new action to a UPS');
+    this.printCommand('nupst action remove <ups-id> <index>', 'Remove an action by index');
+    this.printCommand('nupst action list [ups-id]', 'List all actions (optionally for specific UPS)');
+    console.log('');
+
     // Options
     logger.log(theme.info('Options:'));
     this.printCommand('--debug, -d', 'Enable debug mode for detailed SNMP logging');
@@ -639,6 +680,29 @@ Examples:
   nupst group add         - Create a new group
   nupst group edit dc-1   - Edit group with ID 'dc-1'
   nupst group remove dc-1 - Remove group with ID 'dc-1'
+`);
+  }
+
+  private showActionHelp(): void {
+    logger.log(`
+NUPST - Action Management Commands
+
+Usage:
+  nupst action <subcommand> [arguments]
+
+Subcommands:
+  add <ups-id>                    - Add a new action to a UPS interactively
+  remove <ups-id> <index>         - Remove an action by index (alias: rm, delete)
+  list [ups-id]                   - List all actions (optionally for specific UPS) (alias: ls)
+
+Options:
+  --debug, -d                     - Enable debug mode for detailed logging
+
+Examples:
+  nupst action list               - List actions for all UPS devices
+  nupst action list default       - List actions for UPS with ID 'default'
+  nupst action add default        - Add a new action to UPS 'default'
+  nupst action remove default 0   - Remove action at index 0 from UPS 'default'
 `);
   }
 }