Move account actions (Settings, Downloads, Display preferences, Sign
out) out of the library-only header into a shared AccountMenu anchored in
a global AppHeader, available on every authenticated non-immersive
screen. Add a layoutShell helper deciding where chrome shows, expose
serverName/serverUrl auth stores, and a display view-mode preference. The
settings page also gains the UR-053 WiFi-only toggle.
TRACES: UR-054 | DR-075, DR-076, DR-077
