Prettier 3 (pinned), printWidth 100, double quotes — chosen to match the existing
hand-formatting and minimise reflow. This commit is ONLY the mechanical format pass
(`prettier --write`) plus the config/ignore/scripts, isolated so it never pollutes a
feature diff. Verified behaviour-neutral: typecheck, eslint (0 errors), and vitest
all green before and after. See .git-blame-ignore-revs — `git blame` skips this sha.
Move page/channelView/ytSearch and the history/popstate/title effects out of the
App god component into a new NavigationProvider (split state/actions contexts so
the memo'd VideoCard doesn't re-render on a page/channel switch). App consumes it
via useNavigation/useNavigationActions but still passes the props down for now;
the consumer migration that removes the prop-drilling follows.
peter