Add the canonical AGPL-3.0 text at /LICENSE (with the project copyright
notice on top) and set package.json license to AGPL-3.0-or-later. Chosen
because the trust work reviews AGPL reference implementations and we
reimplement rather than copy; AGPL section 13 source-offer is covered by
the public repo + the License page's source link. Recorded in AGENTS.md.
