fix: remove ESM export from lib.js for QML compatibility

QML's JS engine does not support ES module export/import syntax.
Replace bare export with a CommonJS guard that only runs under Node.js,
so the plugin loads in QML while tests still work.

tailscalectl/lib.js

@@ -15,4 +15,7 @@ function makeExitNodeCommand(hostname) {
     return ["tailscale", "set", "--exit-node=" + hostname]
 }
 
-export { parsePeers, makeExitNodeCommand }
+// CommonJS export for Node.js tests (ignored by QML)
+if (typeof module !== "undefined" && module.exports) {
+    module.exports = { parsePeers, makeExitNodeCommand }
+}

test/lib.test.js

@@ -1,6 +1,7 @@
 import { test } from "node:test"
 import assert from "node:assert"
-import { parsePeers, makeExitNodeCommand } from "../tailscalectl/lib.js"
+import lib from "../tailscalectl/lib.js"
+const { parsePeers, makeExitNodeCommand } = lib
 
 test("parsePeers extracts exitNode from ExitNodeOption", () => {
     const peerMap = {