Consume GameFinished: ELO updates and the game history archive

[TexablePlum]

Move the two effects of a finished game onto the event backbone.

Scope

• user-service: queue + DLQ consumer that validates the envelope and calls the existing
  idempotent ELO path; once verified, remove the gRPC UpdateElo call from game-service and mark
  the rpc deprecated = true in the proto (additive change only - never remove).
• game-service: FinishedGameArchive becomes a consumer on its own queue (idempotent upsert by
  game id), replacing the synchronous archive write.
• Integration tests: publish -> consume -> effect, redelivery without double effects, poison
  messages land in the DLQ.