fix: v2.5.1 — plugin npm runs no longer depend on PATH (Windows update failure)

A Windows self-update failed at "bootstrap": 'npm.cmd' is not recognized.
The update chain runs with the dashboard server's environment, whose PATH
need not reach npm.cmd, and the bootstrap looked npm up through cmd.exe
(shell: true, which also printed DEP0190).

- npmCommand() in scripts/plugin-bootstrap.js runs the npm bundled with the
  running node (npm-cli.js beside process.execPath, Windows and Unix
  layouts) with no shell, and puts that node's directory first on PATH (kept
  under the env's own Path/PATH key) so npm scripts find the same node; npm
  on PATH only when that node ships none
- Used by the runtime install, the UI build (plugin-open.js) and the
  doctor's npm row (plugin-doctor.js)

scripts/plugin-open.js

@@ -29,10 +29,12 @@ const boot = require("./plugin-bootstrap");
 const { resolveDashboardPort } = require("../server/lib/server-info");
 
 const PLUGIN_ROOT = path.resolve(__dirname, "..");
-const NPM = process.platform === "win32" ? "npm.cmd" : "npm";
+const NPM = "npm";
 
-function run(cmd, args, cwd, stdio) {
-  const res = spawnSync(cmd, args, { cwd, stdio, shell: process.platform === "win32" });
+/** `cmd` is always NPM: run through `boot.npmCommand`, never a PATH lookup. */
+function run(_cmd, args, cwd, stdio) {
+  const npm = boot.npmCommand(args);
+  const res = spawnSync(npm.file, npm.args, { cwd, stdio, env: npm.env, shell: npm.shell });
   return res.status === 0;
 }