style(ui): align AI Insights card details toggle with DisclosureButton primitive

Replace custom PlainButton implementation with DisclosureButton in AiInsightsCard.qml to maintain visual consistency with details toggles across the popup and settings pages.

Co-authored-by: Lucenx9 <185146821+Lucenx9@users.noreply.github.com>
bd6c2d9219google-labs-jules[bot] committed on 10/18/2026, 2:18:42 PMparent70c4eff

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