Complete modern C++ foundation structure

[Merd0]

Summary

• Reframed the repository around a C++17 production baseline with C++20/C++23 covered as modern notes instead of default build requirements.
• Expanded EN/TR learning tracks with smart pointers, move semantics, error handling, file I/O, templates, low-level C++, concurrency, and architecture pattern sections.
• Added focused compiling examples for each new topic and strengthened OOP coverage with an object slicing example.
• Added reference indexes and roadmap/standard-policy docs for offline lookup and long-term maintenance.
• Updated CMake targets so all new examples build through the root project, and made project tests work in Release builds without relying on disabled asserts.

Validation

• Ran git diff --check.
• Verified learning path file references exist.
• Verified CMake executable source references exist.
• Ran cmake -S . -B build -DCPP_LEARNING_LAB_WARNINGS_AS_ERRORS=ON.
• Ran cmake --build build --config Release.
• Ran ctest --test-dir build -C Release --output-on-failure.