Replace LICENSE with full AGPL-3.0 text
The previous LICENSE contained only the short FSF boilerplate with
"either version 3 of the License, or (at your option) any later version"
— AGPL-3.0-or-later language that contradicted AGPL-3.0-only declared
in README, pyproject.toml, and SPDX headers in every source file.
Replace with the complete canonical AGPL-3.0 license text from the FSF.
The SPDX-License-Identifier headers in source files remain the
authoritative "only" declaration.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>