doction 0.31.5

Changed

• Relicensed to AGPL-3.0-only. LICENSE carries the verbatim GNU Affero General Public
  License version 3 (661 lines, the FSF text, sha256 0d96a4ff…079abcb0).

  The reason is narrow. doction is hosted for people, and the plain GPL attaches its
  obligation to distributing a copy. An operator never hands anyone a copy, so a modified
  fork could be sold as a hosted service with its changes kept private. The AGPL's section
  13 attaches the obligation to network use instead, which is the case doction actually has.

  Relicensing is not retroactive. Releases through 0.31.3 were published under MIT and
  0.31.4 under GPL-3.0-only. Both grants stand and are not withdrawn: anyone who received
  those versions keeps those terms. AGPL-3.0-only applies from this release onwards.

  Dependency compatibility was re-established for AGPL-3.0 before the change: MIT, BSD-2/3,
  ISC, Apache-2.0, MPL-2.0, PSF-2.0, 0BSD, Zlib, CC0, CC-BY-4.0, Blue Oak 1.0.0, and
  LGPL-3.0-only for psycopg. Nothing in the tree is GPL-2.0-only or proprietary.

Added

• SOURCE_URL and a licence field on GET /api/system, surfaced in Settings, so a running
  instance offers its source to the people using it. It defaults to this repository, so an
  unmodified deployment complies with no configuration, and it is configurable because an
  operator who modifies doction owes their users their source, not this project's.
• A licence-consistency check in make check. The licence is declared in seven places and
  one of them, the published repository description, said "MIT licensed" two releases after
  MIT was replaced without anyone noticing. The check reads pyproject.toml as the single
  authored source and fails when any other declaration disagrees.