fix: Preserve symlink when saving settings.json

[vorburger]

TL;DR

Fixes #10960.

Reviewer Test Plan

Make ~/.gemini/settings.json a symlink instead of a regular file, and have Gemini CLI update it (e.g. by rewriting old to new config).

Testing Matrix

	🍏	🪟	🐧
npm run	❓	❓	✅
npx	❓	❓	❓
Docker	❓	❓	❓
Podman	❓	-	-
Seatbelt	❓	-	-

Linked issues / bugs

Fixes #10960.

[vorburger]

@allenhutchison what's the exact contribution process on this project?

How do I get this tested on platforms that I don't locally have access to?

Humany reviewed by a maintainer?

[allenhutchison]

The contribution process is outlined in https://github.com/google-gemini/gemini-cli/blob/main/CONTRIBUTING.md

Once there is agreement on the bug and the approach we can get the automated test running in other platforms.

[github-actions[bot]]

This pull request has been automatically marked as stale due to 60 days of inactivity. It will be closed in 14 days if no further activity occurs.