feat(cmat): add cmake build for course material

Add a CMakeLists.txt to each exercise directory, included from
cmat/CMakeLists.txt, so every exercise and solution becomes a buildable
target. GUI exercises link the curses-based DOS_Unix implementations on
Unix-like systems; the Windows-specific DOS variants are not compiled.
Exercises without a portable path or with missing dependencies (Boost)
are reported as not available at configure time.

Targets are excluded from the default build and built by name, e.g.
`cmake --build build --target Ex11`, so intentionally buggy exercises
such as Ex21 do not break the default build.

Also fix two portability issues: rename Ex11bug/pole.h to Pole.h for
case-sensitive filesystems and drop the extra Light:: qualification in
SolutionEx71A/Light.h. Document build commands and layout in AGENTS.md.

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

cmat/SolutionEx62Bonus2/Person.h

@@ -0,0 +1,31 @@
+
+
+#ifndef person_H
+#define person_H
+
+#include <string>
+
+#include <boost/serialization/access.hpp>
+#include <boost/serialization/nvp.hpp>
+
+class Person {
+  public:
+    virtual void askForInfo();
+    void display();
+
+  private:
+    virtual void doDisplay();
+
+    std::string firstName;
+    std::string lastName;
+    int age;
+
+    template <class Archive> void serialize(Archive &ar, const unsigned int version) {
+        ar &BOOST_SERIALIZATION_NVP(firstName);
+        ar &BOOST_SERIALIZATION_NVP(lastName);
+        ar &BOOST_SERIALIZATION_NVP(age);
+    }
+    friend class boost::serialization::access;
+};
+
+#endif