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/DOS_Unix/Keyboard_Unix.cpp

@@ -0,0 +1,28 @@
+#include "Keyboard.h"
+#include "CursesObj.h"
+#include "curses.h"
+
+Keyboard::Keyboard() {
+    CursesObj::Instance(); // Force initialization
+
+    nodelay(stdscr, FALSE); // Default to block on getch
+}
+
+bool Keyboard::isCharAvail() {
+    nodelay(stdscr, TRUE); // getch must not block for this polling
+
+    int c; //  DON'T make this 'char'; 'ERR' may be an 'int' - on some systems,
+           //  just like 'EOF'
+
+    bool charWaiting = (c = getch()) != ERR; //  If getch returns ERR, no char
+    //  waiting, otherwise, next char is
+    //  returned
+
+    if (charWaiting)
+        ungetch(c); //  We got a char; put it back! (We just want to know if there
+                    //  is one waiting.)
+
+    return charWaiting;
+}
+
+char Keyboard::getChar() { return getch(); }