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/SolutionEx71ABonus/Light.cpp

@@ -0,0 +1,28 @@
+// ======================================================
+// Light.cpp
+// ======================================================
+
+#include "Light.h"
+#include "PoleVisitor.h"
+#include <iostream>
+
+Light::Light(std::string name, int x, int y, int color) : x(x), y(y), c(color), name(name) {}
+
+Light::~Light() {
+    std::cout << "Deleting light (" << name << ", " << x << ", " << y << ", " << c << ")"
+              << "\n";
+}
+
+void Light::accept(PoleVisitor &pv) { pv.visit(*this); }
+
+void Light::set(LightState new_state) { state = new_state; }
+
+Light::LightState Light::get(void) { return state; }
+
+int Light::getColor(void) { return state == OFF ? 0 : (state == FLASH ? 128 + c : c); }
+
+std::string Light::getString() { return name; }
+
+int Light::getX() { return x; }
+
+int Light::getY() { return y; }