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/Ex42/main.cpp

@@ -0,0 +1,32 @@
+
+
+#include "Keyboard.h"
+#include "Pelican.h"
+#include "Pole.h"
+#include "TimerSet.h"
+
+#include <cctype> // provides toupper()
+
+int main() {
+    Keyboard kbd;
+    Pelican thePelican;
+    Pole pole1(20, 0, thePelican);
+    Pole pole2(40, 0, thePelican);
+
+    char c = 0;
+
+    while (std::toupper(c) != 'Q') { // loop until 'Q' is pressed
+
+        while (!kbd.isCharAvail()) {
+            TimerSet::Instance().pollAllTimers(); // no key press to process, poll the timers
+        }
+
+        c = kbd.getChar(); // get the character
+        if (c == ' ') {
+            // it's a space, so press the WAIT button
+            thePelican.press();
+        }
+    }
+
+    return 0;
+}