remove the list_containers and request_update_meta_inputs MCP tools

Both agent-facing tools go away end to end, with no replacement. This is
an intentional capability removal: agents can no longer enumerate their
own subtree, and can no longer queue a meta-flake input bump.

The system prompt and docs/tools/lifecycle.md land in this same commit
on purpose. A tool named in the prompt but absent from the server makes
agents confidently call something that doesn't exist, and the failure
then surfaces far from its cause.

Removed:

- MCP registrations and bodies (hive-agent-mcp), plus the now-unused
  UpdateMetaInputsArgs.
- Wire variants Request::ListDescendants,
  Request::RequestUpdateMetaInputs and Response::Containers, plus
  ContainerInfo, whose only consumer was that response.
- hive-c0re's handle_list_descendants (its whole module) and
  handle_request_update_meta_inputs, the two dispatch arms, and the
  require_group(agent, "approvals", ...) gate on the meta-inputs verb.
- The stream_enrich emoji entry and argument formatter.
- docs/tools/lifecycle.md (both tools it documented are gone), its two
  referrers, the tool-group tables and the agent-hierarchy prose.

Tool groups are kept, deliberately. ToolGroup::Lifecycle listed exactly
one tool and now lists none — it is vestigial, but the variant stays so
existing meta/capabilities.json grants still parse; retiring it is a
separate decision. ToolGroup::Approvals also listed exactly one tool,
but the group is NOT dead: check_can_cancel_approval still gates
cancel_loose_end's approval-cancel arm on it server-side.

ApprovalKind::UpdateMetaInputs stays too. Nothing in production code
produces it any more, but pre-existing approval rows may still carry it,
and the operator's own path to a meta update is unaffected — the
dashboard's POST /api/meta-update inserts the meta_update job directly,
bypassing approvals entirely.

The two format_ack tests in hive-agent-mcp that named
request_update_meta_inputs were only using it as a label string while
exercising the generic OkWarn/Ok renderer, so they are retargeted to a
surviving tool rather than deleted.

Note hive-c0re's priv_client::list_containers is a different thing (the
host-side privileged container listing behind hive-priv) and is
untouched.

Closes #4591

hive-core-agent-sock/src/lib.rs

@@ -7,7 +7,7 @@
 //! shared payload types it references (`Message`, `LooseEnd`, `Approval`, …)
 //! stay in `hive-sh4re`, which this crate depends on.
 
-use hive_sh4re::container::{ContainerInfo, MatrixIdentity};
+use hive_sh4re::container::MatrixIdentity;
 use hive_sh4re::inbox::{CancelLooseEndKind, DeliveredMessage, InboxRow, LooseEnd};
 use hive_sh4re::journal::JournalPriority;
 use hive_sh4re::manager::SchedulePromptPayload;
@@ -149,13 +149,6 @@ pub enum Request {
     },
 
     // ---- privileged (manager socket only for now) ---------------------------
-    /// *(privileged)* Queue an approval to run `nix flake update [inputs...]`.
-    RequestUpdateMetaInputs {
-        #[serde(default)]
-        inputs: Vec<String>,
-        #[serde(default, skip_serializing_if = "Option::is_none")]
-        description: Option<String>,
-    },
     /// *(privileged)* Queue an approval to add a scheduled prompt.
     RequestSchedulePrompt(SchedulePromptPayload),
     /// *(privileged)* Cancel a scheduled prompt.
@@ -168,12 +161,6 @@ pub enum Request {
     /// plus any owned by an agent in its subtree (everything, for the
     /// operator).
     ListSchedules,
-    /// List the calling agent's subtree — children, their children, and so
-    /// on down, plus the caller itself, which is part of its own subtree.
-    /// Gated by the `lifecycle` tool group. The result includes every known
-    /// member regardless of whether the container is currently
-    /// running — use `running` to distinguish.
-    ListDescendants,
     /// *(privileged)* Fire a scheduled prompt out of band immediately.
     FireScheduleNow { id: i64 },
     /// *(privileged)* Edit an existing schedule's mutable fields.
@@ -276,10 +263,6 @@ pub enum Response {
         full_name: String,
         clone_url: String,
     },
-    /// `ListDescendants` result: all descendant containers, with running
-    /// status. Ordered by topology depth (parents before children), then
-    /// alphabetically within each depth tier.
-    Containers { containers: Vec<ContainerInfo> },
     /// `Recv` result when a graceful stop is pending for this agent
     /// (set by hive-c0re's `GracefulStop` orchestration). Returned in
     /// place of `Messages` — it doubles as the inbound fence: the harness