refactor(editor): streamline ImGui card management across various editors

- Refactored multiple editor classes to ensure that ImGui::End() is always called after ImGui::Begin(), enhancing state management and preventing potential rendering issues.
- Updated the DungeonEditor, GraphicsEditor, ScreenEditor, MessageEditor, MusicEditor, and SpriteEditor to follow this pattern, improving code consistency and reliability.

Benefits:
- Improves the stability of the editor UI by ensuring proper handling of ImGui state.
- Enhances code readability and maintainability by standardizing the usage of ImGui functions across different editor components.

src/app/gui/app/editor_layout.cc

@@ -250,12 +250,14 @@ void EditorCard::SetPosition(Position pos) {
 bool EditorCard::Begin(bool* p_open) {
   // Check visibility flag first - if provided and false, don't show the card
   if (p_open && !*p_open) {
+    imgui_begun_ = false;
     return false;
   }
   
   // Handle icon-collapsed state
   if (icon_collapsible_ && collapsed_to_icon_) {
     DrawFloatingIconButton();
+    imgui_begun_ = false;
     return false;
   }
   
@@ -320,6 +322,9 @@ bool EditorCard::Begin(bool* p_open) {
                              closable_ ? actual_p_open : nullptr, 
                              flags);
   
+  // Mark that ImGui::Begin() was called - End() must always be called now
+  imgui_begun_ = true;
+  
   // Register card window for test automation
   if (ImGui::GetCurrentWindow() && ImGui::GetCurrentWindow()->ID != 0) {
     std::string card_path = absl::StrFormat("EditorCard:%s", title_.c_str());
@@ -332,12 +337,16 @@ bool EditorCard::Begin(bool* p_open) {
 }
 
 void EditorCard::End() {
-  // Check if window was focused this frame
-  focused_ = ImGui::IsWindowFocused(ImGuiFocusedFlags_ChildWindows);
-  
-  ImGui::End();
-  ImGui::PopStyleColor(2);
-  ImGui::PopStyleVar(2);
+  // Only call ImGui::End() and pop styles if ImGui::Begin() was called
+  if (imgui_begun_) {
+    // Check if window was focused this frame
+    focused_ = ImGui::IsWindowFocused(ImGuiFocusedFlags_ChildWindows);
+    
+    ImGui::End();
+    ImGui::PopStyleColor(2);
+    ImGui::PopStyleVar(2);
+    imgui_begun_ = false;
+  }
 }
 
 void EditorCard::Focus() {

src/app/gui/app/editor_layout.h

@@ -98,9 +98,9 @@ class Toolset {
  * tile_card.SetPosition(CardPosition::Right);
  * 
  * if (tile_card.Begin()) {
- *   // Draw tile selector content
- *   tile_card.End();
+ *   // Draw tile selector content when visible
  * }
+ * tile_card.End();  // Always call End() after Begin()
  * ```
  */
 class EditorCard {
@@ -154,6 +154,7 @@ class EditorCard {
   bool first_draw_ = true;
   bool focused_ = false;
   bool* p_open_ = nullptr;
+  bool imgui_begun_ = false;  // Track if ImGui::Begin() was called
   
   // UX enhancements
   bool headless_ = false;  // Minimal chrome, no title bar