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/README.md

@@ -20,7 +20,9 @@ instance on that host — Rust, Conan Exiles, Soulmask, Dune: Awakening.
       crash detection with exit codes, live state in heartbeats
       (integration-tested with real processes + live-NATS contract test)
 - [ ] Phase 1b: RCON trait (WebRCON rust / TCP conan+soulmask), SteamCMD, jailed file manager
-- [ ] Phase 2: Dune Docker adapter (compose lifecycle, RabbitMQ bus, Postgres admin)
+- [~] Phase 2: Dune Docker adapter — **compose lifecycle done** (`docker compose up -d/stop/restart`
+      via the `Supervisor` trait + `DockerComposeSupervisor`); RabbitMQ admin bus + Postgres admin
+      surface deferred. Container crash-detection + state adoption on agent restart land with Phase 3b.
 - [x] Phase 3a: SIGNED self-update — minisign-verified download+swap+relaunch (NATS `update` func); embedded public key; CI signs releases
 - [ ] Phase 3b: service install (systemd/SCM), PID adoption