Define a dedicated `vmvar_t` type for values stored in variable pages
and propagate it through interfaces that expose those values. Keep the
type as int for now so this commit does not change runtime behavior.
This separates VM storage from ordinary int buffers and makes a later
conversion to 16-bit storage mechanically checkable.
With the blocking modal_run(), the game's main loop is frozen while a
menu is open, so the flag's input-suppression and VM-pause checks are
unreachable. Quit requested during a modal is now handled by closing the
modal and letting it propagate through the main loop.
This removes font.h dependency from header files such as ags.h and
nact.h. After this, font.h must be explicitly included in order to use
font functions.
kichikuou