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/snmp/manager.ts

@@ -1,6 +1,6 @@
-import * as snmp from 'net-snmp';
-import type { IOidSet, ISnmpConfig, TUpsModel, IUpsStatus } from './types.js';
-import { UpsOidSets } from './oid-sets.js';
+import * as snmp from "npm:net-snmp@3.20.0";
+import type { IOidSet, ISnmpConfig, TUpsModel, IUpsStatus } from './types.ts';
+import { UpsOidSets } from './oid-sets.ts';
 
 /**
  * Class for SNMP communication with UPS devices