Rename draw() hook to render() so the engine actually calls it

The engine module-lifecycle looks up HOOK_RENDER by the global
name 'render' (engine_module_lifecycle.c:166). The previous draw()
function was a global with no caller, so the editor's UI never
rendered — the engine fell back to its 'no render hook defined'
placeholder.

init.lua

@@ -594,7 +594,7 @@ function update(ctx, dt)
     camera.update(dt)
 end
 
-function draw()
+function render(ctx)
     maps.draw_map()
     ui.draw()
 end