feat(host-agent): Phase 2 — Dune docker-compose adapter via Supervisor trait

Introduce a Supervisor trait (async-trait) so the agent manages games with
different models behind one wire contract. ProcessSupervisor (spawned process:
rust/conan/soulmask) and the new DockerComposeSupervisor (dune) both impl it;
Agent.supervisors is now HashMap<String, Arc<dyn Supervisor>> and instancecmd
dispatch is game-agnostic — start/stop/restart/status identical across games,
selected by a per-game factory in main. InstanceState moved to the shared
supervisor module.

DockerComposeSupervisor drives  against
the instance's compose project, with -f/-p/single-service support and a
configurable compose binary. New [instance.docker_compose] config block.
First cut = lifecycle + cached state; container crash-detection + restart
adoption deferred to Phase 3b (reconcilable with ).

Trait choice (dyn over enum) per Commander: scales to future planes (kubectl,
AMP/podman, SSH) as new struct+impl, no central match.

56 tests green (6 new docker-compose mock-binary tests + 5 refactored process
tests), zero warnings. Live verification pending a real Dune stack.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

corrosion-host-agent/Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "corrosion-host-agent"
-version = "2.0.0-alpha.8"
+version = "2.0.0-alpha.9"
 edition = "2021"
 description = "Corrosion Host Agent — multi-game ops runtime for self-hosted game servers"
 license = "UNLICENSED"
@@ -23,6 +23,7 @@ chrono = { version = "0.4", features = ["serde", "clock"] }
 tracing = "0.1"
 tracing-subscriber = { version = "0.3", features = ["env-filter", "fmt"] }
 anyhow = "1"
+async-trait = "0.1"
 clap = { version = "4.5", features = ["derive"] }
 rand = "0.8"
 tokio-tungstenite = "0.24"