Moves the two tree-style content browser handlers
(--info-zone-tree, --info-project-tree) out of main.cpp into
a new cli_info_tree.{hpp,cpp} module. Both render
Unix-`tree`-style hierarchical views — one drilling into a
single zone (manifest, tiles, creatures, objects, quests,
files) and one giving a bird's-eye view of every zone in a
project with bake/viewer status.
main.cpp shrinks by 201 lines (8,140 to 7,939). The remaining
info-zone/-project-* pairs (bytes, extents, water, density,
audio) form the next natural extraction batch.
