feat(site): show the collection one app at a time on the homepage

[cococool13]

The hero is untouched. Everything under it is new.

What replaced what

Hero (unchanged) → Showcase → tagline reveal → #apps grid → Other Work → Footer

The showcase is a sticky sequence through all four apps. Each panel shows the truest artifact that app has rather than a picture of a window:

Panel	Artifact
Wallpaper	4.6 MB · 95 MB idle · < 1s · 0 background processes
Slim	14 real policy names, and 40 more
Resume	A real render from its own typesetting engine
Clean	Deleted for good / Trash / never touched

The #apps grid stays exactly where it was, so the nav link and the showcase's own links both land somewhere real.

The homepage also had no tagline reveal, which B11 requires. It has one now.

Reuse

The crossfade maths moved to lib/useCrossfade.ts and TemplateSequence now uses it too. That maths had a real bug in it once — panels leaving before the next arrived — so having one copy matters.

Verified in Chrome

• 1440x900: sequence steps 01/04 → 04/04, opacities always sum to 100, never an empty stage
• Hero untouched: Spiral still 96px, same subtitle
• 380px: the sticky version is off and the stacked list renders instead, with artifacts visible

Two fixes from testing. Policy names broke mid-word in the narrower panel, so that artifact is one column now. And on mobile the sticky version was 360vh of scroll for four sentences with every artifact hidden, so below lg it renders stacked.

[Copilot]

Copilot was unable to review this pull request because the user who requested the review has reached their quota limit.