fix: Regression of AgentSummary GQL resolver

[jopemachine]

When using the AgentSummary GQL query in the main branch, the following error occurs.

{
  "data": {
    "agent_summary": null
  },
  "errors": [
    {
      "message": "Agent.batch_load() got an unexpected keyword argument 'scaling_group'",
      "locations": [
        {
          "line": 2,
          "column": 5
        }
      ],
      "path": [
        "agent_summary"
      ]
    }
  ]
}

This PR fixes the above error and additionally resolves several type errors.

Checklist: (if applicable)

• Milestone metadata specifying the target backport version

---

📚 Documentation preview 📚: https://sorna--3045.org.readthedocs.build/en/3045/

---

📚 Documentation preview 📚: https://sorna-ko--3045.org.readthedocs.build/ko/3045/