hive-c0re stops owning scheduled prompts; agents lose the schedule tools

Scheduled prompts are swarm-level now (swarmctl schedule, #4936). The hive
keeps the rows it has only so the operator can copy them over.

- hive-c0re no longer fires anything: the scheduled-prompts worker is gone,
  and with it every create/edit/cancel/pause/resume/fire path (dashboard
  endpoints, agent-socket verbs, the SchedulePrompt approval kind and its
  approve handler). The store keeps open + list; GET /api/schedules stays.
- A v6 approvals migration drops schedule_prompt rows.
- Nothing submits approvals any more, so the submit path goes too:
  Approvals::submit_kind (now a test fixture), the ApprovalAdded dashboard
  event and its emitter.
- Coordinator::push_todo, whose only caller was the worker, goes, and with
  it hive_host_sock::agent_todo_socket and hive-c0re's hive-agent-sock /
  hive-sock-client deps.
- The schedules_changed dashboard event goes; nothing mutates the rows.
- Agents lose request_schedule_prompt, cancel_schedule, fire_schedule_now,
  edit_schedule and list_schedules, the `scheduling` tool group, their
  system-prompt line and their transcript formatters. `remind` is unchanged.

hive-c0re/src/job_queue/exec.rs

@@ -383,10 +383,6 @@ async fn run_destroy_bookkeeping(coord: &Arc<Coordinator>, agent: &str, purge: b
     // (gained one on destroy, lost one on purge — recompute either way).
     coord.rescan_containers_and_emit().await;
     crate::dashboard::emit_tombstones_snapshot(coord).await;
-    // Re-emit the schedules snapshot: the rescan above refreshed the live
-    // roster, so any schedule that still targets the just-destroyed agent now
-    // drops that ghost column live (no page reload needed).
-    coord.emit_schedules_snapshot();
 }
 
 /// Emit this agent's rebuild-complete todo. `ok` is not computed — it is which