feat(#1178): add list_containers tool to AgentServer (topology-scoped to descendants)

hive-ag3nt/prompts/system.md

@@ -45,6 +45,7 @@ Tools (hyperhive surface):
 - `mcp__hyperhive__restart(name)` — *(requires `lifecycle` tool group)* restart a direct child sub-agent (stop + start). The server enforces topology: the call is rejected unless `name` is a direct child of yours per `topology.json`. No approval required.
 - `mcp__hyperhive__kill(name)` — *(requires `lifecycle` tool group)* stop a direct child sub-agent (graceful). Direct children only — server enforces topology. State dir kept; recreating reuses prior config + credentials. No approval required.
 - `mcp__hyperhive__update(name)` — *(requires `lifecycle` tool group)* rebuild a direct child sub-agent: re-applies the current hyperhive flake + agent.nix and restarts it. Direct children only — server enforces topology. No approval required. Idempotent.
+- `mcp__hyperhive__list_containers()` — *(requires `lifecycle` tool group)* list all containers that are topological descendants of this agent (children + their subtrees). Returns each name with running/stopped status, ordered parents-first. Useful before kill/update/restart to check what's under you.
 - `mcp__hyperhive__request_init_config(name, description?)` — *(requires `approvals` tool group)* initialise a brand-new direct child agent's proposed config repo. Queues an `InitConfig` approval; on approval hive-c0re seeds `/agents/<name>/config/agent.nix`. `name` must be a direct child in the topology tree — server enforces. Fails if the config repo already exists (use `request_apply_commit` instead).
 - `mcp__hyperhive__request_apply_commit(agent, commit_ref, description?)` — *(requires `approvals` tool group)* submit a config commit for a direct child agent, queued for operator approval. `agent` must be a direct child in the topology tree — server enforces. `commit_ref` must be a 7-40 char hex sha (not a branch/tag name). On approval hive-c0re rebuilds the container with the pinned commit.