Minor UI improvements

[vswee]

Hero Section

• The hero section has been refreshed with a modern two-column grid, creating balanced spacing and a layout that adapts smoothly to smaller screens.
• Typography has been updated to be larger and bolder, with improved letter spacing and readability.
• The call-to-action buttons (CTAs) now have consistent gaps and alignment, with normalised margins.
• A subtle radial highlight has been added to the background of the page container top for extra visual depth.
• The server image has been enlarged, and a gentle float animation has been applied to the invoice image.
• Responsiveness has been improved with cleaner desktop-to-mobile transitions and refined breakpoints.

Integrations Grid

• A new JavaScript feature introduces a subtle parallax effect on the links in the integrations grid, powered by IntersectionObserver and requestAnimationFrame.
• Movement amplitudes and ranges have been increased, and support has been added for per-item data-depth overrides.
• The grid respects the prefers-reduced-motion setting for accessibility.

Contributors Section

• A staggered “pop-in” animation has been added to the individual grid icons, triggered on scroll-in via IntersectionObserver.
• Animations are implemented as progressive enhancements, falling back gracefully when unsupported.

What is BTCPay Server?

• Section updated to a modern video carousel

Changed Files

• src/js/scripts.js: integrations parallax feature and contributors wave-in animation added; parallax intensity tuned.
• src/css/styles.css: hero layout and typography modernised; background glow introduced; server image size increased; float animation added to the invoice image; CTA spacing and responsive rules refined.
• src/css/page-styles.css: @keyframes popWave and related classes added to stage and trigger the contributors’ wave animation.
• Additionally the render directive for the case studies has been modified to facilitate styling adjustments.

[pavlenex]

Thanks for pushing these updates @vswee, we have it in the backlog to redesign the site from scratch at some point, so we didn't really gave much love to the current itteration. I'd leave it to @dstrukt to check a preview and review.

[dstrukt]

Will get to this asap!

Thanks for looking into this @vswee!

For this PR, and future PRs, one thing that is helpful for the more visual or functional changes is screenshots or a quick screen recording of the work for reviewers.

[pavlenex]

cc @dstrukt