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-agent-mcp/src/mcp/render.rs

@@ -643,12 +643,12 @@ mod tests {
             Ok(hive_core_agent_sock::Response::OkWarn {
                 warnings: vec!["name is reserved".to_owned(), "second thing".to_owned()],
             }),
-            "request_schedule_prompt",
-            "schedule approval queued".to_owned(),
+            "send",
+            "sent to iris".to_owned(),
         );
         // The operation HAPPENED — dropping the success line would read as a
-        // failure and invite a retry that queues a second approval.
-        assert!(out.starts_with("schedule approval queued"));
+        // failure and invite a retry that sends a second message.
+        assert!(out.starts_with("sent to iris"));
         assert!(out.contains("⚠️ name is reserved"));
         assert!(out.contains("⚠️ second thing"));
     }
@@ -659,10 +659,10 @@ mod tests {
         // warning marker would pass the test above.
         let out = format_ack(
             Ok(hive_core_agent_sock::Response::Ok),
-            "request_schedule_prompt",
-            "queued".to_owned(),
+            "send",
+            "sent".to_owned(),
         );
-        assert_eq!(out, "queued");
+        assert_eq!(out, "sent");
         assert!(!out.contains('⚠'));
     }
 }