docs: close dynamic security settings research ticket

The require2fa app extraction successfully implements dynamic security
settings configuration for Two-Factor Authentication:

✅ Runtime configuration via Django admin interface
✅ Uses django-solo pattern for singleton configuration
✅ TwoFactorConfig model allows toggling 2FA enforcement
✅ No settings.py changes required for configuration
✅ Comprehensive security testing (15 tests)
✅ Proper admin interface with field descriptions

This addresses the core research question from #216 about making
security settings configurable through the admin interface.

Closes #216

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Co-Authored-By: Claude <[email protected]>

Author: heysamtexas