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 docker-compose up-d / stop / restart 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 a compose ps probe).

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.lock

@@ -110,6 +110,17 @@ dependencies = [
  "url",
 ]
 
+[[package]]
+name = "async-trait"
+version = "0.1.89"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "9035ad2d096bed7955a320ee7e2230574d28fd3c3a0f186cbea1ff3c7eed5dbb"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "syn",
+]
+
 [[package]]
 name = "atomic-waker"
 version = "1.1.2"
@@ -276,10 +287,11 @@ checksum = "773648b94d0e5d620f64f280777445740e61fe701025087ec8b57f45c791888b"
 
 [[package]]
 name = "corrosion-host-agent"
-version = "2.0.0-alpha.8"
+version = "2.0.0-alpha.9"
 dependencies = [
  "anyhow",
  "async-nats",
+ "async-trait",
  "chrono",
  "clap",
  "futures",