Fix: display error messages when GitHub installations fail to load

[lmac-1]

A user reported that they have an empty dropdown when trying to add a GitHub installation:

My theory is that an API call has failed (e.g due to expired OAuth tokens), and we don't handle these errors. This PR adds proper error handling that displays specific error messages and guides users to reconnect their GitHub account in Settings when needed.

What this PR does

When the GitHub installations API call fails (e.g., due to expired OAuth tokens), users would see an empty dropdown with no explanation. This PR adds:

• Error handling: Displays specific error messages for different failure types (invalid OAuth tokens, generic GitHub errors, network errors)
• User guidance: Provides actionable steps like reconnecting GitHub account in Settings
• Accessibility: ARIA attributes (role="alert", aria-live="polite") for screen reader support
• Security: Limits detailed error output to development environment only
• Test coverage: Comprehensive tests for all error state scenarios

Validation steps

Not a very easy one to validate/test but UI will look something like this, with the GitHub fields disabled, code error messages only visible on dev environments:

If you really want to test the UI, you can ask Claude to comment out some code so you can see the UI in all conditions.

Additional notes for the reviewer

1. The plan for this PR is that once it's merged, I'll get the user to retest and see what error they are getting. Then get them to disconnect and reconnect their GitHub account in order to see if it gets fixed by that.
2. If we can confirm that the reason that error is happening is because of the expired oauth token, we could look how to make that experience a bit better.

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• I have not used AI

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

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 89.52%. Comparing base (5d4762c) to head (ec6f3c3).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4488      +/-   ##
==========================================
- Coverage   89.55%   89.52%   -0.03%     
==========================================
  Files         425      425              
  Lines       20307    20307              
==========================================
- Hits        18185    18180       -5     
- Misses       2122     2127       +5     

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[midigofrank]

@lmac-1 I don't think the issue is about tokens, #4467, if it was about tokens then it would not load on the parent project as well.

I love the idea of putting the warning banner when there is an error while fetching installations though. Maybe we could focus it on the 2 error possibilities:

1. Github is down
2. Access token is expired or user uninstalled the app from github.

There was a "get of jail" link, which would redirect users to github and handle the second scenario:

      <div class="mt-2">
        Can't find the right installation or repository?
        <.link
          target="_blank"
          class="link"
          href={"https://github.com/apps/#{github_config()[:app_name]}"}
        >
          Create/update GitHub installations or modify permissions.
        </.link>
      </div>

[lmac-1]

@midigofrank Hey Frank, thank you for the review! A bit of extra context: I verified with Aisha and it's not just happening for sandboxes, it also happens at the parent project level, I left a comment on #4467. Sorry, I should have put it in the additional notes for reviewer here too. When in a huddle for Aisha I also got her to go to GitHub to check installations and it didn't fix things. Laura also raised the same issue on Friday at project-level and I got her to remove and re-add her GitHub in settings and it fixed the drop down issue.

So perhaps there are 3 scenarios:

1. GitHub is down
2. Access token is expired (will be fixed by removing and readding GitHub in settings)
3. User uninstalled the app from GitHub

Do you want me to do the 'get out of jail free' link for scenario 3? Also do you think that telling the user to go to their settings to remove and readd their GitHub account it a good thing to do to fix 2? Or is there a better way to do this?

[midigofrank]

Aaah, that's good to know @lmac-1 . Yes, I think we should have the get out jail link at the top instead of leading them to the profile page. It is worth testing though