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/SolutionEx61Part2/main.cpp

@@ -0,0 +1,76 @@
+
+#include <exception>
+#include <string>
+#include <vector>
+
+#include "Person.h"
+
+#include "PersonException.h"
+#include <iostream>
+
+#include "memory"
+
+using std::cin;
+using std::cout;
+using std::string;
+using std::exception;
+
+int main() {
+    { // start of extra scope
+        std::vector<std::shared_ptr<Person>> people;
+
+        string namePrompt = "Enter name: ";
+        string name;
+        string agePrompt = "Enter age: ";
+        int age;
+        string salaryPrompt = "Enter salary: ";
+        int salary;
+
+        cout << namePrompt;
+        cin >> name;
+
+        while (name != "q") {
+            try {
+                cout << agePrompt;
+                cin >> age;
+
+                if (!cin) {
+                    cin.clear();
+                    string dummy;
+                    cin >> dummy;
+                    throw PersonException("invalid age");
+                }
+
+                // Person* personPtr = new Person(name, age);
+                std::shared_ptr<Person> personPtr(Person::GetPerson(name, age));
+
+                cout << salaryPrompt;
+                cin >> salary;
+                if (!cin) {
+                    cin.clear();
+                    string dummy;
+                    cin >> dummy;
+                    throw PersonException("invalid salary");
+                }
+
+                personPtr->setSalary(salary);
+
+                people.push_back(personPtr);
+            }
+
+            catch (exception &e) {
+                cout << "PersonException thrown: " << e.what() << '\n';
+            }
+
+            cout << "There are " << Person::GetCount() << " Person(s), " << people.size() << " in vector\n";
+
+            cout << namePrompt;
+            cin >> name;
+        }
+
+    } // end of extra scope, destructor of vector called here
+
+    cout << "There are " << Person::GetCount() << " Person(s) left dangling\n";
+
+    return 0;
+}