Heroe carousel: advance one slide per click and respect loop/nav state

[CySSoO]

Motivation

• Ensure arrow clicks shift the heroe carousel by exactly one slide instead of centering math that could cause multi-slide jumps.
• Respect the block data-loop setting and surface arrow availability for predictable non-loop behavior.

Description

• Change slide translation math in updateSlides() to align to index * slideWidth and clamp it with maxOffset so each arrow click moves one slide width.
• Introduce loop = carousel.dataset.loop !== '0' and add updateNavState() to enable/disable previous/next buttons and set aria-disabled appropriately when not looping.
• Prevent wrapping in goNext()/goPrev() when loop is false and compute .is-prev/.is-next classes separately for loop vs non-loop modes.
• Templating and style tweaks: remove a redundant inline background from the block template and make arrow icon color use currentColor while removing some hardcoded background/colors in the carousel CSS.

Testing

• Started a local PHP dev server with php -S 0.0.0.0:8000 -t ., which started successfully.
• Attempted a Playwright screenshot to verify rendering, but the headless Chromium process crashed in this environment and the screenshot run failed.
• No other automated tests were executed in this rollout.

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Codex Task