feat(canvas): implement popup registry for enhanced menu management

- Introduced a new `PopupRegistry` class to manage persistent popups, improving the organization and lifecycle handling of popups within the canvas.
- Added `canvas_menu.cc` and `canvas_menu.h` to define menu item and section structures, along with rendering functions for a more declarative menu system.
- Updated `canvas.cc` to utilize the new popup registry, ensuring backward compatibility with legacy popup handling during the migration phase.

Benefits:
- Streamlines popup management, enhancing usability and maintainability of the canvas UI.
- Facilitates the addition of complex menu structures and interactions, improving overall user experience.

src/app/gui/canvas/canvas.h

@@ -23,6 +23,8 @@
 #include "app/gui/canvas/canvas_usage_tracker.h"
 #include "app/gui/canvas/canvas_performance_integration.h"
 #include "app/gui/canvas/canvas_interaction_handler.h"
+#include "app/gui/canvas/canvas_menu.h"
+#include "app/gui/canvas/canvas_popup.h"
 #include "imgui/imgui.h"
 
 namespace yaze {
@@ -205,6 +207,10 @@ class Canvas {
   void ClosePersistentPopup(const std::string& popup_id);
   void RenderPersistentPopups();
   
+  // Popup registry access (Phase 3: for advanced users and testing)
+  PopupRegistry& GetPopupRegistry() { return popup_registry_; }
+  const PopupRegistry& GetPopupRegistry() const { return popup_registry_; }
+  
   // Enhanced view and edit operations
   void ShowAdvancedCanvasProperties();
   void ShowScalingControls();
@@ -432,6 +438,11 @@ class Canvas {
   bool context_menu_enabled_ = true;
   
   // Persistent popup state for context menu actions
+  // Phase 3: New popup registry (preferred for new code)
+  PopupRegistry popup_registry_;
+  
+  // Legacy popup state (deprecated - kept for backward compatibility during migration)
+  // TODO(Phase 4): Remove once all editors use popup_registry_ directly
   struct PopupState {
     std::string popup_id;
     bool is_open = false;