Summary

• Split 913-line result.h into 8 focused sub-headers under result/ directory
• Convert result.h to umbrella header for full backward compatibility
• Update documentation with new header structure and include strategies

Changes

New Header Structure

include/kcenon/common/patterns/
├── result.h                      # Umbrella header (backward compatible)
└── result/
    ├── fwd.h                     # Forward declarations, result_state enum
    ├── error_info.h              # error_info struct, error_code alias
    ├── result_core.h             # Result<T> class definition
    ├── optional.h                # Optional<T> class
    ├── result_funcs.h            # Factory/helper functions (ok, make_error)
    ├── error_codes_compat.h      # Backward compatibility aliases
    ├── exception_conversion.h    # exception_mapper, try_catch utilities
    └── result_macros.h           # Convenience macros

Documentation Updates

• Updated BEST_PRACTICES.md with new header structure and include strategies
• Updated CHANGELOG.md with change description

Benefits

1. Improved Compilation Times: Consumers can include only needed headers
2. Better Maintainability: Each header has a focused responsibility
3. Clearer Dependencies: Explicit header organization shows relationships
4. Full Backward Compatibility: Existing #include <.../result.h> unchanged

Test Plan

• All 107 existing tests pass
• Build succeeds on macOS with CMake
• Backward compatibility verified via umbrella header

Closes #243