fix: v2.5.2 — plugin bootstrap exports before it runs (v2.5.1 update crash)

v2.5.1's update died at "bootstrap" on every platform: boot.npmCommand is
not a function. Run as the entry, plugin-bootstrap.js calls bootstrap() →
plugin-open.js, which requires plugin-bootstrap back and got the module.exports
of that moment — {} — because it was assigned at the bottom, below the entry
block. plugin-open.js already exported first for the same reason.

- module.exports moved above the entry block in plugin-bootstrap.js
- A test checks both entry scripts assign module.exports before their entry
  block (it fails on v2.5.1's file); requiring the module, as the other tests
  do, never takes the entry path

package.json

@@ -1,6 +1,6 @@
 {
   "name": "agenthub",
-  "version": "2.5.1",
+  "version": "2.5.2",
   "bin": {
     "agenthub": "bin/agenthub.js"
   },