Make `post-menu-item` components SSR compatible

[alizedebray]

Description:

Hydration errors are caused by at least the fact these are Light DOM components with slots.

How to test:

• Step 1: Isolate the components

  In packages/nextjs-integration/src/app/ssr/page.tsx, comment out all OTHER components. Keep only post-menu-trigger and post-menu-item.

• Step 2: Run E2E tests

  pnpm nextjs:e2e