Shared Experiments Layout
The experiments section previously wrapped each page in its own PageLayout, leading to inconsistent headers and duplicated setup. The app shell introduces a shared layout with a persistent header, conditional back-link navigation, and a bare <main> that individual experiment pages fill.
Cellophane Scoping
The kinetic cellophane background effect was moved into a (showcase) SvelteKit layout group so it only applies to the landing and agents gallery pages. Project-specific experiment pages get a clean background without the visual overhead.