feat: Add layer visibility controls and BG2 layer type selection in DungeonCanvasViewer

- Implemented controls for toggling visibility of background layers BG1 and BG2 in the DungeonCanvasViewer.
- Added a dropdown for selecting the type of BG2 layer, allowing for different rendering effects (Normal, Translucent, Addition, Dark, Off).
- Updated rendering logic to respect visibility settings and apply the selected alpha values for BG2 layer rendering.
- Enhanced debug logging to provide detailed information about bitmap states and rendering processes for both background layers.

src/app/editor/dungeon/dungeon_canvas_viewer.h

@@ -56,6 +56,16 @@ class DungeonCanvasViewer {
   void SetObjectInteractionEnabled(bool enabled) { object_interaction_enabled_ = enabled; }
   bool IsObjectInteractionEnabled() const { return object_interaction_enabled_; }
   
+  // Layer visibility controls
+  void SetBG1Visible(bool visible) { bg1_visible_ = visible; }
+  void SetBG2Visible(bool visible) { bg2_visible_ = visible; }
+  bool IsBG1Visible() const { return bg1_visible_; }
+  bool IsBG2Visible() const { return bg2_visible_; }
+  
+  // BG2 layer type controls
+  void SetBG2LayerType(int type) { bg2_layer_type_ = type; }
+  int GetBG2LayerType() const { return bg2_layer_type_; }
+  
   // Set the object to be placed
   void SetPreviewObject(const zelda3::RoomObject& object) {
     object_interaction_.SetPreviewObject(object, true);
@@ -95,6 +105,11 @@ class DungeonCanvasViewer {
   // Object interaction state
   bool object_interaction_enabled_ = true;
   
+  // Layer visibility controls
+  bool bg1_visible_ = true;
+  bool bg2_visible_ = true;
+  int bg2_layer_type_ = 0;  // 0=Normal, 1=Translucent, 2=Addition, etc.
+  
   // Palette data
   uint64_t current_palette_group_id_ = 0;
   uint64_t current_palette_id_ = 0;