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/Ex11/PelicanTimer.cpp

@@ -0,0 +1,10 @@
+
+#include "PelicanTimer.h"
+
+PelicanTimer::PelicanTimer(Pelican &target, TargetFunc targetFunc) : myTarget(target), myTargetFunc(targetFunc) {}
+
+void PelicanTimer::tick() {
+    if (isExpired()) {
+        (myTarget.*myTargetFunc)();
+    }
+}