Add Django middleware template

[WeJaWi]

Summary

• add a new templates/django-middleware package for APort verification in Django apps
• include settings-driven path protection plus a @require_policy view decorator
• add a mockable client adapter, minimal example project, README docs, and pytest-django coverage
• list the Django template in the root README

Closes #14

Verification

• python3 -m venv /tmp/aport-django-venv
• . /tmp/aport-django-venv/bin/activate
• python -m pip install --upgrade pip setuptools wheel
• python -m pip install -e ".[dev]"
• pytest -q

Result: 10 passed, 1 warning

Bounty

This PR is for the $50 USD bounty in #14.