Following up on the feedback from PR #62, this PR addresses the remaining cleanup items suggested by @scrrlt:

• Tooling: Re-added --exit-zero to the ruff pre-commit hook. This ensures that the hook doesn't block contributor workflows with existing lint violations while still applying automatic fixes where possible.
• Clarity: Explicitly re-added completion_cost to the litellm imports in token_tracker.py (both solve and research versions) to ensure clarity and consistency, addressing concerns about potential downstream breakages.
• Best Practices: Removed the sys.path.insert hack in tests/core/test_prompt_manager.py and pruned now-unused sys and pathlib imports.
• Verification: Confirmed that display_manager.py is clean of unused imports (as verified by ruff check).

These changes help maintain a healthy codebase and a smoother workflow for contributors.