Move the modules (Feed/Channels/Playlists/Stats) out of the avatar dropdown into a
persistent left sidebar with icon+label entries; collapses to a thin icon rail
(persisted in localStorage). Account actions (About, Sign out, admin badge) move to a
popover at the sidebar bottom; Settings is a rail entry. Header is now a contextual top
bar (sync status, feed scope + search or page title, language, notifications) — logo and
account menu removed from it. New nav.json strings (HU/EN/DE). First step of Epic N.
