guest sdk: room lifecycle declarations — resumable / ephemeral / resident

[BCook98]

Kit half of the room-lifecycle-modes change (engine half follows; design in the platform spec workspace).

GameMeta.Lifecycle — a trailing presence-guarded byte after the large-room meta section:

value	meaning
LifecycleResumable (0, default)	hibernate on abandonment, player-driven resume — today's behavior, byte-compat for every existing artifact
LifecycleEphemeral	after the abandonment grace the room ends and disposes — no snapshot, no Resume entry (casual social rooms; the grace still covers connection blips)
LifecycleResident	one long-lived room per slug — persistent worlds; granted by the platform per slug, ungranted declarations behave as resumable

• ABI major stays 2; older payloads decode as resumable; hosts treat unknown values as resumable.
• Encode-time validation (both SDKs, fail-fast): undefined values rejected; resident + MinPlayers > 1 rejected (a resident room runs with zero members).
• Rust crate mirrors field/enum/validation; goldens extended and the lifecycle suffix cross-checked against the actual Go encoder.
• Docs: ABI.md (the byte + zero-member posture), GUIDE.md "Choosing a lifecycle" (including End() as the resident world-reset primitive).
• go test ./... and cargo test green.

Sequencing: merge + tag v2.7.0 → engine PR pins it → catalog games declare ephemeral.

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