Moves the two water-layer audit handlers (--info-zone-water,
--info-project-water) out of main.cpp into a new
cli_info_water.{hpp,cpp} module. Both aggregate liquid data
(water/ocean/magma/slime) across MH2O chunks; the project
variant rolls per-zone counts into a project-wide total with
height range and per-type histogram.
main.cpp shrinks by 209 lines (7,463 to 7,254). Both --json
output modes preserved for capacity-planning pipelines.
