fix(logs): preserve subdirectory in _validate_log_path (#2194)

[mrveiss]

Summary

• Fixed _validate_log_path silently dropping subdirectory components via Path.name
• Changed function to accept filename: str and pass directly to validate_relative_path
• Updated all 5 callers to pass filename instead of LOG_DIR / filename
• Tests passing (2 log-related tests)

Closes #2194

[github-actions]

✅ SSOT Configuration Compliance: Passing

🎉 No hardcoded values detected that have SSOT config equivalents!