When AUTH_ENABLED=false, the anonymous user was assigned the "user" role
which lacks settings:write permission, making all settings saves return
403. Since no admin exists when auth is disabled, settings were
permanently read-only. Promote the anonymous user to "admin" so the
single user has full control of the instance.
Also adds DEFAULT_TOOL_VIEW env var (sidebar|fullscreen) following the
existing DEFAULT_THEME pattern, seeded via ensureDefaultSettings() on
first boot.
Closes#135