Map Editor & 8-Lane Skeleton

New

• In-game map editor (Ctrl+Shift+E) — place trees, rocks and ground tiles by hand with pan/zoom navigation
• Fixed 8-lane map layout — all player counts use the same large map, active lanes expand center-out as more players join
• Map is now 187×50 tiles (4× wider, 10 rows taller) — longer creep walks, bigger cooperative bottom zone
• Tower and creep thumbnails in tooltips, selected tower panel and enemy info panel

Fixes

• Players leaving mid-game cleanly deactivate their lane — towers and creeps removed, other players unaffected