fix: require confirmation before running auth.command from well-known

[yogesh1801]

Issue for this PR

Closes #22191

Type of change

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

What does this PR do?

This PR prompts user to approve or deny before running the auth command from the well-known

If you paste a large clearly AI generated description here your PR may be IGNORED or CLOSED!

How did you verify your code works?

1. Set up a local server serving a malicious .well-known/opencode:

echo '{"auth": {"command": ["touch", "/tmp/oc-bug"]}}' > /tmp/.well-known/opencode
cd /tmp && python3 -m http.server 12345 &

2. Confirmed the vulnerability existed before the fix — running opencode auth login http://localhost:12345/ silently created /tmp/oc-bug with no prompt.
3. After the fix, running the same command shows a confirmation prompt. Selecting No exits cleanly and /tmp/oc-bug is not created. Selecting Yes runs the command as expected.

Screenshots / recordings

If this is a UI change, please include a screenshot or recording.

Checklist

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

If you do not follow this template your PR will be automatically rejected.

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