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/nupst.ts

@@ -1,12 +1,12 @@
-import { NupstSnmp } from './snmp/manager.js';
-import { NupstDaemon } from './daemon.js';
-import { NupstSystemd } from './systemd.js';
-import { commitinfo } from './00_commitinfo_data.js';
-import { logger } from './logger.js';
-import { UpsHandler } from './cli/ups-handler.js';
-import { GroupHandler } from './cli/group-handler.js';
-import { ServiceHandler } from './cli/service-handler.js';
-import * as https from 'https';
+import { NupstSnmp } from './snmp/manager.ts';
+import { NupstDaemon } from './daemon.ts';
+import { NupstSystemd } from './systemd.ts';
+import { commitinfo } from './00_commitinfo_data.ts';
+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 * as https from "node:https";
 
 /**
  * Main Nupst class that coordinates all components