Fix simple image slider centering and spacing

[CySSoO]

Motivation

• Ensure the active image in the Prettyblock "Simple Image" slider is truly centered between the navigation arrows and prevent adjacent images from being visually cut off by increasing item gaps.

Description

• Updated updateTrackPosition in views/js/everblock-slider.js to account for state.gap when computing the track translateX, so the active item is centered correctly between the arrows by using state.index * (state.itemWidth + state.gap) in the offset calculation.
• Increased spacing in views/css/everblock.css by changing .ever-slider-track column-gap from 1.5rem to 2rem on desktop and from 1rem to 1.25rem at the tablet breakpoint to reduce image cropping.

Testing

• Attempted an automated visual check by taking a screenshot with Playwright, but the local server was unreachable and the run failed with net::ERR_EMPTY_RESPONSE.
• No unit or integration tests were executed.

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Codex Task