[ci] npm publishing manifest format is malformed.

[ditman]

The upload_manifest.mjs script that creates the manifest file to trigger the exit gate NPM publishing workflow is generating something like:

{
  "publish_all": true,
  "packages": {
    "@a2ui/angular": "0.9.1",
    "@a2ui/lit-explorer": "0.9.0",
    "@a2ui/lit": "0.9.3",
    "@a2ui/markdown-it": "0.0.4",
    "@a2ui/react": "0.9.1",
    "@a2ui/visual-parity": "0.8.0",
    "@a2ui/web_core": "0.9.2"
  }
}

But that format is wrong, we need either:

{
  "publish_all": true
}

Or, to allow-list each package:

{
  "publish_all": false,
  "publishing_groups": [
    { 
      "namespace": "@a2ui", 
      "packages": [
        {
          "name": "angular",
          "version": "0.9.1"
        },
        {
          "name": "lit-explorer"
          "version": "0.9.0"
        },
        ...
      ]
    }
  ]
}

Update the publish script so we produce a valid manifest file.

[ditman]

/cc @jacobsimionato @josemontespg (Thanks @joycebrum!)