fix(desktop-electron): avoid startup loading hang

[aiulms]

Issue for this PR

Closes #23308

Type of change

• Bug fix
• New feature
• Refactor / code improvement
• Documentation

What does this PR do?

This fixes an Electron desktop startup hang on macOS where the app can stay on Just a moment... even after the sidecar is ready.

The change does two things:

• keeps the preload init-step listener alive until the loading flow reaches done
• removes a startup wait in the Electron path that can block on sqlite migration state that is not resolved on this path

How did you verify your code works?

I built the patched Electron desktop app locally on macOS arm64 and launched it with a clean local state. Before the change it stayed on the loading window. After the change it opened into the app successfully.

Screenshots / recordings

UI loading fix only. No screenshot attached.

Checklist

• I have tested my changes locally
• I have not included unrelated changes in this PR

[github-actions]

Thanks for your contribution!

This PR doesn't have a linked issue. All PRs must reference an existing issue.

Please:

1. Open an issue describing the bug/feature (if one doesn't exist)
2. Add Fixes #<number> or Closes #<number> to this PR description

See CONTRIBUTING.md for details.

[github-actions]

The following comment was made by an LLM, it may be inaccurate:

Found 1 potential related PR:

PR #19281: fix(desktop): add timeout guards to prevent Windows startup hang
#19281

This PR addresses a similar issue - a desktop startup hang, though on Windows instead of macOS. Both PRs are fixing platform-specific startup loading hangs in the Electron desktop app and likely involve similar root causes or complementary fixes. Note: This is a different PR (not a duplicate of #23307), but addresses the same general problem space.

[github-actions]

Thanks for updating your PR! It now meets our contributing guidelines. 👍

[github-actions]

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