Wrap map draw in camera.begin/finish so world-space transforms apply

Without the camera scope, maps.draw_map() rendered the map at
screen coords starting at (0,0) regardless of camera.set_target,
and screen_to_world's inverse produced bogus cell coords (mouse
in screen-center mapped to top-left tile). Spine-prototype's
render() shows the right pattern: world-space draws inside
camera.begin/finish, screen-space overlays after.

init.lua

@@ -595,6 +595,8 @@ function update(ctx, dt)
 end
 
 function render(ctx)
+    camera.begin()
         maps.draw_map()
-    ui.draw()
+    camera.finish()
+    ui.draw()   -- screen-space overlays after camera ends
 end