Move section separator into creditsSection and remove outer redundant
Kirigami.Separator. When creditsSection was hidden but other additional
sections (resetCreditsSection, providerCostSection, etc.) were visible,
the outer separator rendered alongside the inner separator of the next
section, creating stacked duplicate separator lines. Each additional section
now consistently owns its top separator.

Co-authored-by: google-labs-jules[bot] <161369871+google-labs-jules[bot]@users.noreply.github.com>
Co-authored-by: Lucenx9 <185146821+Lucenx9@users.noreply.github.com>