chore: Finalize refactoring changes and compatibility layers

Complete the modularization with compatibility and type improvements:

  - src/core/context.py: Add type annotations for PortingContext

  - src/core/modifiers/framework_modifier.py: Convert to compatibility shim

    - Import from new modular framework package

    - Maintain backward compatibility for existing code

  - src/core/rom.py: Remove (replaced by src/core/rom/ package)

Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>

Author: toraidl