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/SolutionEx31/Main.cpp

@@ -0,0 +1,69 @@
+
+#include "Pixel.h"
+
+#include <algorithm>
+#include <iostream>
+#include <vector>
+using namespace std;
+
+void pixelPrint(const Pixel &pixel) { pixel.print(); }
+
+int main() {
+
+    // From Ex 3.1
+
+    // preamble
+    Pixel pixel0;
+    cout << "Preamble:" << endl;
+    pixel0.print();
+    cout << endl;
+
+    Pixel pixel1(1, 2);
+    Pixel pixel2(3, 3);
+    Pixel pixel3(2, 4);
+    Pixel pixel4(5, 2);
+    Pixel pixel5(4, 2);
+
+    // 3.1 part 1
+    cout << "3.1 Part 1:" << endl;
+    vector<Pixel> pixelVec;
+    pixelVec.push_back(pixel1);
+    pixelVec.push_back(pixel2);
+    pixelVec.push_back(pixel3);
+    pixelVec.push_back(pixel4);
+    pixelVec.push_back(pixel5);
+
+    for (unsigned int i = 0; i < pixelVec.size(); ++i) {
+        pixelVec[i].print();
+    }
+    cout << endl;
+
+    // 3.1 part 2
+    cout << "3.1 Part 2:" << endl;
+    for (vector<Pixel>::iterator iter = pixelVec.begin(); iter != pixelVec.end(); ++iter) {
+        iter->print();
+    }
+    cout << endl;
+    for (vector<Pixel>::reverse_iterator r_iter = pixelVec.rbegin(); r_iter != pixelVec.rend(); ++r_iter) {
+        r_iter->print();
+    }
+    cout << endl;
+
+    vector<Pixel> pixelVec2{pixel1, pixel2, pixel3, pixel4, pixel5};
+    for (const Pixel &p : pixelVec2) {
+        p.print();
+    }
+    cout << endl;
+
+    // 3.1 part 3
+    cout << "3.1 Part 3:" << endl;
+    for_each(pixelVec.begin(), pixelVec.end(), pixelPrint);
+    cout << endl;
+    sort(pixelVec.begin(), pixelVec.end());
+    for_each(pixelVec.begin(), pixelVec.end(), pixelPrint);
+    cout << endl;
+
+    // insert code here ***************************************
+
+    return 0;
+}