optional: nicer apollo errors for lightning users

[taylordowns2000]

Description

This PR makes it possible to show more detailed errors to AI chat users.

Validation steps

1. Boot up lightning with a faulty AI assistant token.
2. Try to send a message to the AI chat.
3. See a nicer error.

AI Usage

Please disclose whether you've used AI anywhere in this PR (it's cool, we just
want to know!):

• I have used Claude Code
• I have used another model
• I have not used AI

You can read more details in our
Responsible AI Policy

Pre-submission checklist

• I have performed an AI review of my code (we recommend using /review
  with Claude Code)
• I have implemented and tested all related authorization policies.
  (e.g., :owner, :admin, :editor, :viewer)
• I have updated the changelog.
• I have ticked a box in "AI usage" in this PR