chore: disable ssr for showcase app (#563)

# Motivation

Without disabling SSR we would not be able to build the showcase case
app once the component `InfiniteScroll` is effectively used in the UI.
This is because `IntersectionObserver` is not a known NodeJS property.

# Notes

PR that uses the `InfiniteScroll` in the UI is #562.

# Changes

- Disable SSR which we do not used in first place anyway
- Added wait in the segments E2E as the screenshots seem to be generated
earlier following this change (see test
https://github.com/dfinity/gix-components/actions/runs/12868805408/job/35876230527)

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src/routes/+layout.ts

@@ -1 +1,2 @@
 export const prerender = true;
+export const ssr = false;