Add content description for lock icon on Set Up button

[Gosling-dude]

Summary

Adds a content description to the lock icon shown on the “Set up” button in the Add Card bottom sheet to improve TalkBack accessibility.

Details

The lock icon previously had no content description, so TalkBack did not announce it. This change adds a localized accessibility label so screen readers correctly convey the security context.

Fixes #10356

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