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/main.rs

@@ -45,9 +45,7 @@ mod workers;
 pub(crate) use agent_config::{capabilities, limits, resource_limits, tool_groups, topology};
 pub(crate) use stats::{container_stats, hive_stats, host_stats, otel_metrics, warnings};
 pub(crate) use stores::{approvals, broker, build_logs, db, power, scheduled_prompts};
-pub(crate) use workers::{
-    agent_sockets, auto_update, crash_watch, knowledge, mcp_sockets, scheduled_prompts_worker,
-};
+pub(crate) use workers::{agent_sockets, auto_update, crash_watch, knowledge, mcp_sockets};
 
 use coordinator::{Coordinator, HiveEnv, ServeConfig};
 
@@ -240,7 +238,7 @@ fn submit_periodic_sweep(
 }
 
 /// Start the coordinator daemon: open the broker, run migrations, spawn
-/// background tasks (auto-update, vacuums, crash-watcher, scheduled-prompts,
+/// background tasks (auto-update, vacuums, crash-watcher,
 /// dashboard), then serve the admin socket until a signal arrives.
 #[allow(
     clippy::too_many_lines,
@@ -433,10 +431,6 @@ async fn cmd_serve(
     // run_reconcile call register_agent on start; kill/destroy call
     // unregister_agent. No recurring poll needed — c0re owns the listeners.
     mcp_sockets::sync_on_start(coord.clone()).await;
-    // Scheduled-prompts worker: drains due scheduled_prompts rows
-    // and fans the body out to each active target's inbox. See
-    // scheduled_prompts_worker.rs.
-    scheduled_prompts_worker::spawn(coord.clone());
     // Job-queue scheduler: drives the global DAG queue (rebuild /
     // meta-update / spawn / power ops). Concurrency comes from the
     // build-slot count + per-agent leases inside the queue, not from