Eliminate all code, tests, and utilities related to the legacy 'unclaimed' user
scope. All API endpoints, document and audiobook storage, and access logic now
require a valid authenticated userId and only operate on resources owned by that
user. Remove related helper functions, test cases, and conditional flows for
anonymous/unclaimed data. Update types, client APIs, and UI logic to reflect
that only 'user' scope is supported. This simplifies ownership checks and
removes ambiguity around document and audiobook access.
Move changelog version check effect from SettingsModal to a new
scheduleChangelogCheck utility for improved modularity and testability.
Add unit tests for changelog check scheduling behavior.
