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/SolutionEx61InterimSolution/Person.cpp

@@ -0,0 +1,37 @@
+#include "Person.h"
+#include "PersonException.h"
+#include "YoungPerson.h"
+#include <iostream>
+
+using std::cout;
+
+Person::Person(std::string name, int age) : name(name), age(age) {
+    if (age < 0) {
+        throw PersonException("negative age");
+    }
+
+    cout << "Person ctor\n";
+    Count++;
+}
+
+Person::Person(const Person &) {
+    cout << "Copy ctor\n";
+    Count++;
+}
+
+Person::~Person() {
+    cout << "Dtor\n";
+    Count--;
+}
+
+void Person::setSalary(int sal) {
+    if (sal < 0) {
+        throw PersonException("negative salary");
+    }
+
+    salary = sal;
+}
+
+int Person::GetCount() { return Count; }
+
+int Person::Count = 0;