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/Ex11bug/TimerSet.cpp

@@ -0,0 +1,24 @@
+ 
+
+
+
+#include "TimerSet.h"
+#include "Timer.h"
+
+TimerSet theTimerSet;
+
+
+
+TimerSet::TimerSet() : timersInUse(0), previousTime(time(&previousTime)) {}
+
+void TimerSet::addATimer(Timer *t) { timers[timersInUse++] = t; }
+
+void TimerSet::pollAllTimers() {
+    std::time_t timeNow;
+    if (time(&timeNow) > previousTime) {
+        previousTime = timeNow;
+        for (int i = 0; i < timersInUse; ++i) {
+            timers[i]->tick();
+        }
+    }
+}