Modular CLI & Validator Refactor

[cclint]

Highlights:

• Refactored the validator into a modular Python package to improve maintainability, testability, and CLI usability.
• Introduced a proper CLI entry point via csb_validator.cli with support for both crowbar and trusted-node validation modes.
• All core logic split into discrete modules:
• runner.py handles async orchestration
• validator_crowbar.py and validator_trusted.py encapsulate validation logic
• pdf_writer.py generates summary reports
• line_mapper.py enables precise line-level error mapping
• added main.py for support of python -m csb_validator

Fixes:

• resolved import path and Any type hint errors
• removed sys.path hacks and redundant imports in tests