Refactor DungeonEditor and related components for improved object management and UI enhancements

- Replaced vertical separators with standard separators in the EditorManager's menu bar for consistency.
- Introduced a new room selection callback mechanism in DungeonRoomSelector to facilitate room selection events.
- Enhanced DungeonEditor with drag-and-select functionality for object placement, improving user interaction.
- Added an object browser in DungeonObjectSelector for better object management and preview capabilities.
- Streamlined object rendering and selection processes, ensuring a more intuitive editing experience.

src/app/editor/editor_manager.cc

@@ -892,7 +892,7 @@ void EditorManager::DrawMenuBar() {
         SetTooltip("Sessions: %zu active\nClick to switch between sessions", sessions_.size());
       }
       SameLine();
-      ImGui::SeparatorEx(ImGuiSeparatorFlags_Vertical);
+      ImGui::Separator();
       SameLine();
     }
     
@@ -927,7 +927,7 @@ void EditorManager::DrawMenuBar() {
     
     // Settings and version (using pre-calculated positioning)
     SameLine(GetWindowWidth() - total_right_width);
-    ImGui::SeparatorEx(ImGuiSeparatorFlags_Vertical);
+    ImGui::Separator();
     SameLine();
     
     PushStyleColor(ImGuiCol_Button, ImVec4(0, 0, 0, 0));