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/SolutionEx71A/TimerSet.cpp

@@ -0,0 +1,37 @@
+#include "TimerSet.h"
+#include "Timer.h"
+#include <iostream>
+
+//  Member functions
+
+TimerSet::TimerSet()
+    : previousTime(time(&previousTime)), pollingThread([this]() { poll10Hz(); }) // Exercise 5.1 start thread
+{
+    pollingThread.detach(); // let it die on its own, without join
+}
+
+// Exercise 5.1 new function
+void TimerSet::poll10Hz() {
+    std::chrono::duration<int, std::milli> pause(100);
+    while (true) {
+        std::this_thread::sleep_for(pause);
+        pollAllTimers();
+    }
+}
+
+void TimerSet::addATimer(Timer *t) { timers.push_back(t); }
+
+void TimerSet::pollAllTimers() {
+    std::time_t timeNow;
+    if (time(&timeNow) > previousTime) {
+        previousTime = timeNow;
+        for (auto it = timers.begin(); it != timers.end(); it++) {
+            (*it)->tick();
+        }
+    }
+}
+
+TimerSet &TimerSet::Instance() {
+    static TimerSet pInstance;
+    return pInstance;
+}