Theme provider now initializes to the SSR-stable default and reconciles
the stored preference in a mount effect instead of reading localStorage
in the useState initializer — closes the same React #418 hydration seam
the sidebar already fixed (the inline script still handles the pre-paint
class, so no FOUC). Add a process-wide Intl formatter cache and route the
per-row workout/medication list helpers through it so a formatter is
constructed once per (locale, options) rather than once per row per
render.
