feat(editor): undo object placement, snap to ground, keyboard shortcuts

- Ctrl+Z in Object/NPC mode undoes last placement (50-deep stack)
- "Snap Ground" button raycasts straight down to place object on terrain
- Useful for objects placed too high or moved off terrain surface
- Undo stack adjusts indices when objects are removed mid-stack

tools/editor/editor_app.cpp

@@ -212,10 +212,17 @@ void EditorApp::processEvents() {
                     }
                 }
                 if (sc == SDL_SCANCODE_Z && (event.key.keysym.mod & KMOD_CTRL)) {
-                    if (event.key.keysym.mod & KMOD_SHIFT)
-                        terrainEditor_.redo();
-                    else
-                        terrainEditor_.undo();
+                    if (mode_ == EditorMode::Sculpt) {
+                        if (event.key.keysym.mod & KMOD_SHIFT)
+                            terrainEditor_.redo();
+                        else
+                            terrainEditor_.undo();
+                    } else if (mode_ == EditorMode::PlaceObject || mode_ == EditorMode::NPC) {
+                        if (!(event.key.keysym.mod & KMOD_SHIFT) && objectPlacer_.canUndoPlace()) {
+                            objectPlacer_.undoLastPlace();
+                            objectsDirty_ = true;
+                        }
+                    }
                 }
             }
             if (!io.WantCaptureKeyboard)
@@ -554,6 +561,21 @@ void EditorApp::setGizmoAxis(TransformAxis axis) {
         viewport_.getGizmo().setTarget(sel->position, sel->scale);
 }
 
+void EditorApp::snapSelectedToGround() {
+    auto* sel = objectPlacer_.getSelected();
+    if (!sel || !terrain_.isLoaded()) return;
+
+    // Cast ray straight down from object position
+    rendering::Ray ray;
+    ray.origin = sel->position + glm::vec3(0, 0, 500);
+    ray.direction = glm::vec3(0, 0, -1);
+    glm::vec3 hitPos;
+    if (terrainEditor_.raycastTerrain(ray, hitPos)) {
+        sel->position.z = hitPos.z;
+        objectsDirty_ = true;
+    }
+}
+
 void EditorApp::resetCamera() {
     camera_.setPosition(glm::vec3(0.0f, 0.0f, 300.0f));
     camera_.setYawPitch(0.0f, -30.0f);

tools/editor/editor_app.hpp

@@ -61,6 +61,7 @@ public:
 
     void startGizmoMode(TransformMode mode);
     void setGizmoAxis(TransformAxis axis);
+    void snapSelectedToGround();
     TransformGizmo& getGizmo() { return viewport_.getGizmo(); }
     bool shouldOpenContextMenu() const { return openContextMenu_; }
     void clearContextMenuFlag() { openContextMenu_ = false; }

tools/editor/editor_ui.cpp

@@ -360,8 +360,10 @@ void EditorUI::renderObjectPanel(EditorApp& app) {
 
             if (changed) app.markObjectsDirty();
 
-            if (ImGui::Button("Delete", ImVec2(100, 0))) placer.deleteSelected();
+            if (ImGui::Button("Snap Ground", ImVec2(100, 0)))
+                app.snapSelectedToGround();
             ImGui::SameLine();
+            if (ImGui::Button("Delete", ImVec2(100, 0))) placer.deleteSelected();
             if (ImGui::Button("Duplicate", ImVec2(100, 0))) {
                 PlacedObject copy = *sel;
                 copy.uniqueId = 0;

tools/editor/object_placer.cpp

@@ -29,6 +29,8 @@ void ObjectPlacer::placeObject(const glm::vec3& position) {
     obj.selected = false;
 
     objects_.push_back(obj);
+    undoStack_.push_back(static_cast<int>(objects_.size() - 1));
+    if (undoStack_.size() > 50) undoStack_.erase(undoStack_.begin());
     LOG_INFO("Placed ", (activeType_ == PlaceableType::M2 ? "M2" : "WMO"),
              ": ", activePath_, " at (", position.x, ",", position.y, ",", position.z, ")");
 }
@@ -93,6 +95,19 @@ void ObjectPlacer::deleteSelected() {
     selectedIdx_ = -1;
 }
 
+void ObjectPlacer::undoLastPlace() {
+    if (undoStack_.empty()) return;
+    int idx = undoStack_.back();
+    undoStack_.pop_back();
+    if (idx >= 0 && idx < static_cast<int>(objects_.size())) {
+        if (selectedIdx_ == idx) selectedIdx_ = -1;
+        else if (selectedIdx_ > idx) selectedIdx_--;
+        objects_.erase(objects_.begin() + idx);
+        // Adjust remaining undo indices
+        for (auto& i : undoStack_) { if (i > idx) i--; }
+    }
+}
+
 void ObjectPlacer::syncToTerrain() {
     if (!terrain_) return;
 

tools/editor/object_placer.hpp

@@ -57,6 +57,10 @@ public:
     float getPlacementScale() const { return placementScale_; }
     void setPlacementScale(float s) { placementScale_ = s; }
 
+    // Undo last placement
+    bool canUndoPlace() const { return !undoStack_.empty(); }
+    void undoLastPlace();
+
 private:
     uint32_t nextUniqueId();
 
@@ -65,6 +69,7 @@ private:
     PlaceableType activeType_ = PlaceableType::M2;
 
     std::vector<PlacedObject> objects_;
+    std::vector<int> undoStack_; // indices of recently placed objects
     int selectedIdx_ = -1;
     uint32_t uniqueIdCounter_ = 1;
     float placementRotY_ = 0.0f;