refactor: Modernize architecture and apply canonical C++ project layout

[NoaLand]

Context & Objective

This PR completely modernizes the legacy C++ delivery codebase to serve as a high-quality, realistic assessment tool for Consultant+ level candidates.

The primary goal of this refactoring was to elevate the architectural design, C++ language standards, and project structure to industry best practices, while intentionally preserving (and highlighting) the core business logic "code smells" for candidates to identify during the interview.

Enterprise-Grade C++ Project Structure

• Canonical C++ Layout (Pitchfork): Implemented strict physical separation of interface and implementation by introducing dedicated include/ and src/ directories across all modules.
• Namespaced Includes: Headers are now packaged under enterprise-standard paths (e.g., #include <tw/delivery/service/CartService.h>), preventing header clashes and evaluating the candidate's familiarity with large-scale C++ codebases.
• CMake Boundary Enforcement: Refactored CMakeLists.txt to strictly enforce module boundaries using target_include_directories with PUBLIC and PRIVATE visibility scopes.

Key Architectural & C++ Enhancements

• Clean Architecture Implementation: Dismantled the monolithic rest/ directory and restructured the project into strict layers (core/, dto/, infra/adapters/, service/, app/).
• Anti-Corruption Layer (ACL): Isolated the 3rd-party JSON library (nlohmann::json) inside infra/adapters/.
• Modern C++ Memory Management:
  • Fixed fatal Object Slicing and memory leaks in the Product hierarchy by introducing std::shared_ptr and virtual destructors.
  • Applied the Sink-it pattern (std::move) and std::string_view for zero-copy efficiency.
  • Enforced the Rule of Zero by removing broken, manually-written copy constructors.
• Command Dispatcher Pattern: Refactored main.cpp's messy switch-case into a scalable std::unordered_map router with robust stream state handling.