Adjust duo agent platform widget feature preview state

What does this MR do and why?

Adjust duo agent platform widget feature preview state

• adjust for enhanced wording and clarity when in the feauture preview off only state.
• adjusted the spacing in the widget to match designs.
• see https://gitlab.com/gitlab-org/gitlab/-/issues/565473#note_2736972253
• see https://gitlab.com/gitlab-org/gitlab/-/issues/565473

Screenshots or screen recordings

Screen_Recording_2025-09-08_at_2.08.46_PM

before	after
more spacing in widget around body and buttons
more spacing in widget around body and buttons

How to set up and validate locally

see !202833 (merged)

MR acceptance checklist

Evaluate this MR against the MR acceptance checklist. It helps you analyze changes to reduce risks in quality, performance, reliability, security, and maintainability.

Related to #565473