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

deno.json

@@ -0,0 +1,34 @@
+{
+  "name": "@serve.zone/nupst",
+  "version": "4.0.0",
+  "exports": "./mod.ts",
+  "tasks": {
+    "dev": "deno run --allow-all mod.ts",
+    "compile": "deno task compile:all",
+    "compile:all": "bash scripts/compile-all.sh",
+    "test": "deno test --allow-all tests/",
+    "check": "deno check mod.ts",
+    "fmt": "deno fmt",
+    "lint": "deno lint"
+  },
+  "lint": {
+    "rules": {
+      "tags": ["recommended"]
+    }
+  },
+  "fmt": {
+    "useTabs": false,
+    "lineWidth": 100,
+    "indentWidth": 2,
+    "semiColons": true
+  },
+  "compilerOptions": {
+    "lib": ["deno.window"],
+    "strict": true
+  },
+  "imports": {
+    "@std/cli": "jsr:@std/cli@^1.0.0",
+    "@std/fmt": "jsr:@std/fmt@^1.0.0",
+    "@std/path": "jsr:@std/path@^1.0.0"
+  }
+}