mcp: remove the restart/kill/start/update/get_logs agent verbs

Container lifecycle from inside an agent goes away: an agent no longer
starts, stops, restarts or rebuilds a container in its subtree, and no
longer reads another container's journal. Those are operator actions —
the dashboard and hivectl keep their own paths to the same job-queue
and hive-priv plumbing, which is why none of that machinery is removed
here, only the five MCP verbs and what they alone reached.

What went with them: the `Request` variants and `Response::Logs` on the
agent socket, the five tool definitions and their arg structs, the four
lifecycle handlers plus `handle_get_logs`, and `require_descendant` —
the topology guard those five were the only remaining callers of.
`ToolGroup::Diagnostics` goes too: `get_logs` was its only tool, so it
would otherwise be a grantable group that grants nothing. `lifecycle`
stays, now carrying `list_containers` alone.

An agent that gets a `needs_update` or `container_crash` helper event
has no remedy of its own left, so the system prompt and the docs now
send it to the operator instead of to a tool that no longer exists.

Refs #4480

docs/agent-lifecycle/approvals.md

@@ -617,10 +617,10 @@ root agent. Variants (`hive_sh4re::manager::HelperEvent`):
   tombstone, three `POLL_INTERVAL`s — closes the race where a
   lifecycle op finishes between two crash-watch polls and the
   container shows briefly as "stopped without transient" before
-  the next start). The root agent can `start` it again or escalate.
+  the next start). The root agent escalates to the operator, who
+  starts it again from the dashboard.
 - `NeedsUpdate { agent }` — sub-agent's recorded flake rev is
-  stale. The root agent calls `update(name)` to rebuild — idempotent,
-  no approval required.
+  stale. The operator rebuilds it from the dashboard.
 
 The remaining lower-urgency lifecycle notices — `Rebuilt`, `Killed`,
 `Destroyed`, `NeedsLogin`, `LoggedIn` — are "FYI, check