chore(license): migrate MPL-2.0 → AGPL-3.0-or-later (Joshua co-dev)

Replace LICENSE file with canonical AGPL-3.0-or-later text and update package
metadata (Cargo.toml/package.json/deno.json/mix.exs/pyproject.toml where
present) to declare the new SPDX identifier.

Rationale: Joshua co-dev.

Part of estate-wide metadata cleanup 2026-05-26.

Author: hyperpolymath