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.

hive-sh4re/README.md

@@ -1,7 +1,7 @@
 # hive-sh4re
 
 The **shared payload vocabulary** between `hive-c0re` and the in-container
-harness — the common types (`Message`, `Approval`, `LooseEnd`, `HelperEvent`, …)
+harness — the common types (`Message`, `LooseEnd`, `HelperEvent`, …)
 that the per-socket wire protocols are built from. The request/response
 _envelopes_ themselves now live in the per-socket crates (below); this crate
 holds the payloads they carry.
@@ -17,7 +17,7 @@ in all of `hive-sh4re`:
 - `hive-priv-sock` — the privileged-helper socket
 
 Those crates re-export or reference the payload types that still live here
-(`Approval`, `Message`, `LooseEnd`, …).
+(`Message`, `LooseEnd`, …).
 
 ## Modules