License under AGPL-3.0-or-later, bump to 0.2.3

- `LICENSE`: full GNU AGPL v3 text (canonical, via GitHub's license API).
- `pyproject.toml`: `license = "AGPL-3.0-or-later"`, `license-files = ["LICENSE"]`.
- `README.md`: "License" section now points at LICENSE and notes the
  network-use clause that distinguishes AGPL from GPL.
- README earlier mentioned MIT — that was a placeholder, never the
  intended license.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: jdrumgoole