Phase 1-2: Migrate to Deno with npm: and node: specifiers

- Created deno.json configuration
- Updated all imports to use npm:net-snmp@3.20.0
- Changed all Node.js built-in imports to node: specifiers
- Updated all .js extensions to .ts in imports
- Created mod.ts as Deno entry point
- Ready for Phase 3: CLI simplification

ts/cli/ups-handler.ts

@@ -1,7 +1,7 @@
-import { execSync } from 'child_process';
-import { Nupst } from '../nupst.js';
-import { logger } from '../logger.js';
-import * as helpers from '../helpers/index.js';
+import { execSync } from "node:child_process";
+import { Nupst } from '../nupst.ts';
+import { logger } from '../logger.ts';
+import * as helpers from '../helpers/index.ts';
 
 /**
  * Class for handling UPS-related CLI commands