feat(editor): minimap, patrol path editing, flatten height picker

- Minimap window: 16x16 chunk grid colored by average height
  (blue=low, green=mid, brown=high, blue overlay=water)
- NPC patrol path UI: add waypoints at cursor, view path list,
  delete individual points or clear entire path
- Sculpt flatten "Pick" button: click to set target height from
  cursor position instead of typing manually
- Height range displayed in minimap footer

tools/editor/editor_ui.hpp

@@ -32,6 +32,7 @@ private:
     void renderWaterPanel(EditorApp& app);
     void renderNpcPanel(EditorApp& app);
     void renderContextMenu(EditorApp& app);
+    void renderMinimap(EditorApp& app);
     void renderPropertiesPanel(EditorApp& app);
     void renderStatusBar(EditorApp& app);