feat(cmat): implement Ex41 observer pattern

Refactor the Pelican crossing exercise to use the Observer
pattern: Pelican acts as Subject and each Pole observes it,
replacing direct calls through the owned Pole pointer.

Co-authored-by: Qwen 3.8 27B <qwen3.8_27b-q3_k_xl@lmstudio.local>

cmat/Ex41/Pelican.h

@@ -7,12 +7,14 @@
 #ifndef PELICAN_H
 #define PELICAN_H
 
+#include "Subject.h"
+
 class PelicanTimer;
 class Pole;
 
-class Pelican {
+class Pelican : public Subject {
   public:
-    Pelican(int x, int y);
+    Pelican();
     ~Pelican();
 
     // call when the WAIT button has been pressed
@@ -39,8 +41,6 @@ class Pelican {
     // indicates whether the WAIT light should be on
     bool pressed;
 
-    Pole *myPole;
-
     // Timer that indicates when the lights should change
     PelicanTimer *myTimer;