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/CursesObj.cpp

@@ -0,0 +1,51 @@
+#include "CursesObj.h"
+#include "curses.h"
+
+CursesObj::CursesObj() {
+    //  Colours 0 to 7 are defined by curses. But we need grey as well
+    //  Define a suitable constant here (and create the colour later)
+    const int COLOR_GREY = 8;
+
+    initscr(); /* initialize the curses library */
+    nonl();    /* tell curses not to do NL->CR/NL on output */
+    cbreak();  /* take input chars one at a time, no wait for \n */
+    nodelay(stdscr, FALSE);
+    noecho(); /* echo input - in color */
+    curs_set(0);
+    intrflush(stdscr, FALSE);
+
+    if (has_colors()) {
+        start_color();
+
+        /*
+         * Simple color assignment, often all we need.  Color pair 0 cannot
+         * be redefined.  This example uses the same value for the color
+         * pair as for the foreground color, though of course that is not
+         * necessary:
+         */
+        init_pair(1, COLOR_RED, COLOR_BLACK);
+        init_pair(2, COLOR_GREEN, COLOR_BLACK);
+        init_pair(3, COLOR_YELLOW, COLOR_BLACK);
+        init_pair(4, COLOR_BLUE, COLOR_BLACK);
+        init_pair(5, COLOR_CYAN, COLOR_BLACK);
+        init_pair(6, COLOR_MAGENTA, COLOR_BLACK);
+        init_pair(7, COLOR_WHITE, COLOR_BLACK);
+
+        //  Create 'grey' and then use it as foreground colour
+        init_color(8, 1, 333, 333);
+
+        init_pair(8, COLOR_GREY, COLOR_BLACK);
+    }
+}
+
+CursesObj::~CursesObj() {
+    clear();
+    refresh();
+    endwin();
+}
+
+CursesObj &CursesObj::Instance() {
+    static CursesObj instance;
+
+    return instance;
+}