fix(animations): mobile scroll animation — earlier trigger, no reverse on scroll-up (the opacity)

[Katotodan]

Problem

On small devices, scrub-based ScrollTrigger animations caused two issues: content appeared late because the animation range spanned a large portion of the viewport, and every entrance/recession animation reversed when scrolling back up — hurting both UX and CPU.

Solution

Introduces a thin mobile-detection layer with no structural changes to the desktop experience.

isMobile — a matchMedia('(max-width: 768px)') flag computed once on load, used as a branching condition throughout.
stConfig(trigger, start, end) — a helper that returns a ScrollTrigger config object. On mobile it shifts start ~5% earlier and sets toggleActions: "play none none none" (time-based, no scrub). On desktop it returns the original scrub config unchanged.

scrubEach() — updated with the same mobile branch inline.

Recession effects (hero-glass wrapper, hero-section, demo-section) are guarded with if (!isMobile) so the fade/scale-out animations don't run — and therefore don't reverse — on small screens.

Behaviour after this PR

	Desktop	Mobile
Entrance animation	Scrub-linked (unchanged)	Plays once as element enters viewport
Scroll-up reversal	Yes (scrub)	No (toggleActions: "play none none none")
Recession effects	Yes	Skipped
Trigger timing	Unchanged	~5% earlier

Testing

Verify on a real device (≤768px width) by scrolling down (content animates in promptly) and back up (content stays visible, no jank).

Use the preview link on a mobile device to view the changes

• This PR fixes #Scroll animations on mobile feel sluggish and reverse unexpectedly on scroll-up #160
  Part of Javascript: Improve animation performance #146

Signed commits

• Yes, I signed my commits.

[github-actions]

PR Preview Action v1.6.3
Preview removed because the pull request was closed.
2026-04-23 13:00 UTC

[Bhumikagarggg]

https://github.com/user-attachments/assets/cfcf2137-39ee-4700-9d3a-a07ca35328b3
Still : content appeared late?

[Bhumikagarggg]

@Katotodan Thank you for your contribution! Let's discuss this during the website call tomorrow at 5:30 PM IST | 7 AM CST Add it as an agenda item to the meeting minutes, if you would 🙂