Move theme toggle, notifications, app switcher, and user profile from
the top header bar into the sidebar. App switcher at the top (scope
switch), utilities at the bottom. Header now only shows on mobile for
the hamburger menu.
Sidebar and content header were too transparent — content bled through.
Bump from bg-*/70 to bg-*/90 with backdrop-blur-xl for a subtle glass
effect that's still readable.
Apply the same backdrop-blur-2xl + semi-transparent bg treatment from
the AppLauncher dropdown to the sidebar and content header. Matches
the Ciphera design language: bg-white/70 dark:bg-neutral-900/70 with
supports-[backdrop-filter] progressive enhancement. Soften all borders
to /60 opacity.
