v0.3.1

Tooling and documentation; the module itself behaves as in 0.3.0. Freedoom
gives the dev gateway a free registered-mode IWAD, so the bring-your-own-WAD
path is now tested all the way to the engine loading a PWAD, and the four
committed engines are proven reproducible on every change.

Added

• Freedoom as the dev gateway's free registered-mode IWAD:
  ops/fetch-freedoom.sh (pinned 0.13.0, checksummed against the release's
  signed CHECKSUM, never committed or shipped) plus mustry-test.wad, a
  56-byte PWAD of our own, and an e2e test that requires the engine to load
  it with -file on freedoom2.wad. README: "Mods without buying Doom II"
  and a Freedoom row in the bring-your-own-WAD table. (#17)
• CI: the Engines reproducible workflow rebuilds the four committed engines
  from the pinned sources in the emsdk image and fails on any byte of
  difference (on engine changes, weekly, on demand). The e2e suite also runs,
  informationally, against inductiveautomation/ignition:latest
  (IGNITION_IMAGE in docker-compose.yml).
• Docs: four games throughout (README, reference, engine README, notices),
  new pictures (launcher, Heretic, Hexen, Strife, the how-to page) from a
  repeatable screenshot job, the dev-gateway section lists the fixture
  scripts and what the suite covers.

Changed

• DoomRelayTickets is DoomTickets (it has issued WAD download tickets
  since 0.2.0); the operator-WAD resolution rules moved out of the component
  into resolveFetched() in doomLogic.ts, unit-tested. No behaviour change.