fix(editor): terrain raycast on rough terrain, keyboard shortcuts, context menu

- Raycast AABB now uses actual min/max vertex heights per chunk
  instead of fixed ±200 padding (fixes misses on sculpted terrain)
- Right-click context menu opens correctly (deferred popup via flag
  since ImGui::OpenPopup must be called within ImGui frame)
- Keyboard shortcuts: G=Move, R=Rotate, T=Scale, X/Y=axis lock,
  Escape=deselect, Delete works in any mode for objects/NPCs
- Delete key now removes selected NPC in NPC mode too

tools/editor/editor_ui.cpp

@@ -592,6 +592,10 @@ void EditorUI::renderWaterPanel(EditorApp& app) {
 }
 
 void EditorUI::renderContextMenu(EditorApp& app) {
+    if (app.shouldOpenContextMenu()) {
+        ImGui::OpenPopup("ObjectContextMenu");
+        app.clearContextMenuFlag();
+    }
     if (ImGui::BeginPopup("ObjectContextMenu")) {
         auto* sel = app.getObjectPlacer().getSelected();
         if (!sel) { ImGui::EndPopup(); return; }