style: apply variant 'destructive' to sign-out buttons

[jaycodev]

Description

This PR updates the sign-out buttons to visually reflect a destructive action:

• Adds variant='destructive' to the Sign out DropdownMenuItem.
• Updates the confirmation dialog's sign-out button to use variant='destructive' as well.

This improves visual consistency and better communicates the destructive nature of the action to the user.

Before	After

Types of changes

• Others (any other types not listed above)

Checklist

• I have read the Contributing Guide

Further comments

Minor UI/style change only — no logic or functionality affected.
All checks (pnpm lint, pnpm build) pass successfully.

Related Issue

N/A

[satnaing]

Thanks for the contribution.