Switch packaging to hatchling, add scan CLI, optional extras, and include policy assets

[Jeffrin-dev]

Motivation

• Use a modern build backend by switching the project to Hatchling and reduce core install size by moving heavy libraries to optional extras.
• Ensure the package exposes the shadowaudit console script and provide a simple CLI scan subcommand to allow ad-hoc PII scans without loading optional heavyweight deps.
• Include the policy YAMLs in source distributions so policies/* are packaged and available at install time.

Description

• Added a [build-system] section to pyproject.toml to use hatchling and moved non-essential libraries into [project.optional-dependencies] groups ner and siem, while keeping minimal dependencies in the core install.
• Registered the console script shadowaudit = "shadowaudit.cli:main" in pyproject.toml and preserved CLI behavior for policy check, report, and proxy.
• Extended shadowaudit/cli.py with a scan subcommand that uses PIIScanner and prints JSON output, and updated serialization to fall back to dataclasses.asdict when model_dump is not available.
• Added MANIFEST.in to include policies/gdpr.yaml, policies/hipaa.yaml, and policies/pci_dss.yaml in source distributions and added tests/test_cli_scan.py to cover the new scan command.

Testing

• Ran pytest tests/test_cli_policy_check.py tests/test_cli_proxy.py tests/test_cli_report.py tests/test_cli_scan.py and all included tests passed (5 passed).
• Ran pytest for the full suite which showed two existing unrelated failures in tests/test_policy_and_secrets.py (these are from an external detect-secrets API mismatch and were not caused by these changes).
• Executed the CLI smoke flows python -m shadowaudit.cli scan "Reach me at alice@example.com", python -m shadowaudit.cli policy check policies/gdpr.yaml, and python -m shadowaudit.cli report --format gdpr --from 2026-01-01 --to 2026-01-31, all of which produced expected output.
• Attempted python -m pip install -e . but the build step failed in this environment because hatchling could not be downloaded due to network/proxy restrictions, and pytest --cov=... --cov-fail-under=80 could not be run because pytest-cov is not installed in the current environment.

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Codex Task