The reader and login pages use +layout@ breakouts to escape the (root)
shell, so anything mounted in (root)/+layout.svelte never reaches them.
ModeWatcher was mounted there and duplicated in login/+layout@.svelte,
which left the reader's theme toggle inert: it flipped the store but
nothing wrote .dark onto <html>.
Mount both once at the top-level +layout.svelte instead, which every
route inherits regardless of breakouts.
patrick
hiperman