Delete the src/app tree, next.config.ts, next-env.d.ts, and the Next-only
guard/header components. Port AppShell/Sidebar/Topbar to react-router and
mount them as a DashboardLayout route over all authenticated routes. Strip
'use client' directives, move globals.css up from the deleted app/ tree,
rewrite tsconfig for Vite/Bundler resolution, drop the next dependency.
Test fixes the port surfaced: jsdom v29 has no window.matchMedia (sidebar
breakpoint) so setup.ts stubs it; the router-boundary specs render inside
ThemeProvider because the chrome's ThemeToggle requires the context.
fred
70c7311a46