hive-c0re: remove the approvals subsystem

Nothing submits an approval since scheduled prompts left hive-c0re, so the
queue only acted on rows written before that.

- hive-c0re: the approvals store and its migrations, approve/deny/
  resolve actions, the ResolveApproval tail node (and meta_update's
  approval_id), POST /api/approve and /api/deny, the approval views on
  /api/state, the approval_resolved dashboard event, the orphan GC,
  destroy/purge failing pending rows, and the approval rows in
  get_loose_ends. DestroyBookkeeping loses the purge flag, which only
  worded the approval-failure note.
- The CancelLooseEnd request goes: its only hive-c0re arm was the
  approval one. cancel_loose_end handles reminder and todo in the harness.
- Wire types: hive_sh4re::approvals (ReminderStats moves to inbox),
  LooseEnd::Approval, CancelLooseEndKind, HelperEvent::ApprovalResolved,
  ToolGroup::Approvals, HostRequest::{Pending,Approve,Deny} and
  HostResponse.approvals. HOST_SOCK_VERSION goes to 2 for the removed
  field.
- hivectl loses the approvals verbs; docs/tools/hivectl-cli.md is
  regenerated.
- The system prompt drops approval_resolved.
- The approvals table stays in broker.sqlite, unread, the same way the
  operator_questions table was left when its store was removed.
- An `approvals` entry still in tool-groups.json is skipped with a warning
  by ToolGroup::parse_list, like any unknown group.
- docs/agent-lifecycle/approvals.md is renamed to config-changes.md so the
  code's doc pointers resolve; its content follows in the docs commit.

hivectl/src/cli.rs

@@ -82,13 +82,6 @@ pub enum Cmd {
     /// under `hivectl agent <name>`. Idempotent — safe to re-run. Once
     /// enabled, `hivectl agent <name> quota show`/`quota set` work.
     QuotaEnable,
-    /// Operator approval queue: list, approve, or deny pending requests.
-    ///
-    /// Needs the hive-c0re daemon running.
-    Approvals {
-        #[command(subcommand)]
-        cmd: ApprovalsCmd,
-    },
     /// WireGuard inter-hive mesh setup helpers.
     ///
     /// Generate this hive's mesh key and print the nix to enable the mesh,
@@ -476,23 +469,6 @@ pub enum AgentQuotaCmd {
     },
 }
 
-/// Operator approval queue: list, approve, or deny pending requests.
-#[derive(Subcommand)]
-pub enum ApprovalsCmd {
-    /// List pending approval requests submitted by agents.
-    Pending,
-    /// Approve a pending request by id; the action runs immediately.
-    Approve {
-        /// Approval id (from `hivectl approvals pending`).
-        id: i64,
-    },
-    /// Deny a pending request by id.
-    Deny {
-        /// Approval id.
-        id: i64,
-    },
-}
-
 #[derive(Subcommand)]
 pub enum SubvolCmd {
     /// Convert a plain-dir agent state root into a btrfs subvolume in