fix(auth): prevent redundant scrollbar on login page in Firefox

[api2062]

Description

Fixes a Firefox-specific UI issue where the login/auth screen shows a redundant scrollbar even when content does not overflow.

The auth layout uses the Scroll component from folds, which can behave as overflow: scroll with thin scrollbars. This can cause Firefox to render a visible scrollbar track unnecessarily.
This change sets overflow: auto on the auth Scroll container so the scrollbar only appears when actual overflow exists.

Fixes #2776

Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings

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[api2062]

I have read the CLA Document and I hereby sign the CLA

[api2062]

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