Sidebar remains stable during navigation

The sidebar no longer flickers when navigating between pages.

Bug Fixes

The sidebar used to flicker or reset when navigating between pages due to how Next.js reconciles Suspense boundaries in parallel routes. The fix moves the Suspense boundary from the route slot to the layout (which stays mounted across soft navigation) and uses CSS layering so the loading skeleton only appears on hard refreshes. You now get a smooth, stable sidebar as you navigate between pages and projects.