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/Ex71/CompanyEntry.cpp

@@ -0,0 +1,19 @@
+#include <iomanip>
+#include <iostream>
+
+#include "CompanyEntry.h"
+#include "EntryVisitor.h"
+
+CompanyEntry::CompanyEntry(std::string name, std::string category, std::string phone)
+    : Entry(name), _category(category), _phone(phone) {}
+
+void CompanyEntry::print(std::string indent) const {
+
+    std::cout << indent << "Company: " << getName() << " <" << _category << "> " << _phone << '\n';
+}
+
+std::string CompanyEntry::getPhone() const { return _phone; }
+
+std::string CompanyEntry::getCategory() const { return _category; }
+
+void CompanyEntry::accept(EntryVisitor &v) const { v.visit(*this); }