🎨 Palette: Add keyboard accessibility for hover trailers

[google-labs-jules]

Palette 🎨 added keyboard accessibility to the Hover Trailer plugin.

Why: Previously, trailer previews were only triggered by mouse hover (mouseenter/mouseleave), leaving keyboard users without access to this feature. Additionally, the preview overlay could potentially interfere with keyboard navigation.

What:

1. Added focusin and focusout event listeners to movie cards.
2. Implemented logic to check if focus moves within the card (e.g., from card container to a "Play" button inside) to maintain the preview state.
3. Added aria-hidden="true" and tabindex="-1" to the injected iframe/video elements so they are purely visual/ambient and don't trap focus.

Testing:

• Verified code changes by inspection of the injected JavaScript logic.
• Ensured no regression in existing mouse behavior logic (timers and state are shared correctly).

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PR created automatically by Jules for task 11792076038738597963 started by @Fovty

[google-labs-jules]

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