gen3_box 1.2.1

Added

• In-game updates. The manifest now declares its github repo, which is
  what the launcher's updater reads and what the "Find mods" tab installs
  from. Releases are named gen3_box-<version>.zip, the exact name
  ModUpdate.pickZipAsset prefers — a test asserts the manifest and that
  file name still agree, because the two drifting apart would silently
  demote the updater to "grab whatever zip is attached".