Export only z from zod external wrapper

Changed from exporting all of zod to only exporting the z object we actually use.

Before:
  module.exports = require('zod')

After:
  const { z } = require('zod')
  module.exports = { z }

This is more explicit and follows the principle of only exporting what's needed.

Status: 5/6 test suites passing (ipc.test.ts still has vitest resolution issue)

Author: jdalton

src/external/zod.js

@@ -1 +1,2 @@
-module.exports = require('zod')
+const { z } = require('zod')
+module.exports = { z }