refactor: use modern ROOT dictionary generation in ship_add_library

[olantwin]

Replace FairRoot's scope-variable-driven FAIRROOT_GENERATE_DICTIONARY() with the modern target-based CMake. This:

• Invokes rootcling directly instead of via a shell script wrapper
• Reads include directories from target properties via generator expressions
• Removes all scope variable manipulation (LIBRARY_NAME, HDRS, DICTIONARY, LINKDEF, LIBRARY_OUTPUT_PATH, INCLUDE_DIRECTORIES, SYSTEM_INCLUDE_DIRECTORIES)
• Requires library creation before dictionary generation (reorder in ship_add_library)

Checklist

• Changelog updated (if applicable)
• Commit message follows conventional commits
• CI checks pass