Improve install UX and packaging readiness

[Justadudeinspace]

Motivation

• Make installation for end users and CI simpler by adding a curl/wget-friendly bootstrap and recommending uv/pipx flows.
• Avoid shipping heavy optional deps by keeping PDF/reporting optional and only loading reportlab at runtime when needed.
• Ensure runtime dependencies required by core features (audit encryption) are declared so installed packages won't break at runtime.
• Align project metadata and scripts with modern packaging norms and a consistent Python minimum (3.9+).

Description

• Add install.sh that prefers uv tool install, falls back to pipx, then pip --user for curl/wget bootstrap installs.
• Make PDF output lazy-imported in the CLI (_write_pdf_report) and emit a clear message if reportlab is missing.
• Add cryptography>=42.0.0 to pyproject.toml and requirements.txt so audit/encryption features are available when installed.
• Bump minimum Python guidance to 3.9 across the entrypoint and install/bootstrap scripts and switch pyproject.toml license to SPDX license + license-files.

Testing

• Ran formatting with ruff format . which succeeded (1 file reformatted).
• Ran ruff check . which surfaced existing lint issues in the repo (known pre-existing failures).
• Attempted pytest (in this environment pytest failed due to pytest-cov/inifile coverage options not resolved).
• Built distributions with python -m build (created sdist and wheel), installed the wheel into a temporary venv and verified dat --help succeeded (smoke test pass).

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Codex Task

[Justadudeinspace]

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[Justadudeinspace]

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