Pointer in the editor; new screenshots and an editor section in the README

Scenes for the screenshots come from export_scenes (src/scenes.rs) and are
taken with tools/screenshots.py in the Playwright image.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/main.rs

@@ -27,6 +27,8 @@ mod rival;
 mod render3d;
 mod rooms;
 mod save;
+#[cfg(test)]
+mod scenes;
 mod blocks;
 mod mscript;
 mod settings;
@@ -1900,6 +1902,9 @@ fn editor_frame(app: &mut App, menu: &mut Menu, cloud: &mut Cloud, r3d: &mut R3d
         g.map.activate();
     }
     let act = ed.frame(gfx, r3d, dt, now);
+    // the game draws its own pointer (the system one is hidden)
+    ui::begin_ui();
+    ui.draw_cursor(gfx, &app.game, now, true);
     match act {
         editor::EdAction::None => {}
         editor::EdAction::Close => {