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/src/config.rs

@@ -10,6 +10,7 @@ use serde::Deserialize;
 use std::collections::HashSet;
 use std::path::{Path, PathBuf};
 
+use crate::docker_compose::DockerComposeConfig;
 use crate::rcon::RconConfig;
 use crate::steamcmd::SteamcmdConfig;
 
@@ -76,6 +77,10 @@ pub struct InstanceConfig {
     /// validate = false).
     #[serde(default)]
     pub steamcmd: Option<SteamcmdConfig>,
+    /// Docker-compose settings for container-managed games (Dune). Absent =
+    /// defaults apply (compose file in the instance root, project = instance id).
+    #[serde(default)]
+    pub docker_compose: Option<DockerComposeConfig>,
 }
 
 impl InstanceConfig {