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/src/schedule_timer.rs

@@ -4,9 +4,8 @@
 //! `agent-schedules` KV bucket. This task reads that key every
 //! [`POLL_INTERVAL`] with the one subject the agent's own queue credential is
 //! granted there (`swarm_queue_client::agent_schedules::read_own`), and fires
-//! each due schedule as the same `schedule`-subsystem todo, keyed
-//! `schedule:<id>`, that hive-c0re's schedule worker pushes. The wake path
-//! is the todo store's.
+//! each due schedule as a `schedule`-subsystem todo, keyed `schedule:<id>`.
+//! The wake path is the todo store's.
 //!
 //! **Fire times come from the schedule alone**: `anchor + k * interval`
 //! ([`Schedule::latest_slot`]). Rewriting the list, or changing a body,
@@ -43,7 +42,7 @@ use crate::todos::Todos;
 /// longest a fire can lag its slot, and a change can take to reach the agent.
 const POLL_INTERVAL: Duration = Duration::from_secs(10);
 
-/// The todo subsystem and source hive-c0re's schedule worker uses.
+/// The todo subsystem and source a schedule fire carries.
 const SUBSYSTEM: &str = "schedule";
 const SOURCE: &str = "scheduled";
 
@@ -161,7 +160,7 @@ fn tick(
     }
 }
 
-/// Push `schedule` as the todo hive-c0re's worker pushes, and wake the turn
+/// Push `schedule` as a todo, and wake the turn
 /// loop when it is new or reopened.
 fn push_todo(todos: &Todos, wake: &Notify, schedule: &Schedule) -> bool {
     let key = format!("schedule:{}", schedule.id);
@@ -364,11 +363,10 @@ mod tests {
         assert_eq!(fired(&l, &slots, 1005), ["a body"]);
     }
 
-    /// The same todo hive-c0re's worker pushes, so the wake path does not
-    /// change: subsystem `schedule`, key `schedule:<id>`, source
-    /// `scheduled`, and a reopen once the agent acked the previous fire.
+    /// A fire is subsystem `schedule`, key `schedule:<id>`, source
+    /// `scheduled`, and reopens once the agent acked the previous fire.
     #[test]
-    fn a_fire_is_the_hive_c0re_schedule_todo() {
+    fn a_fire_is_the_schedule_todo() {
         let todos = Todos::open(Path::new(":memory:")).unwrap();
         let wake = Notify::new();
         let s = schedule("abcdefgh", 1000, Some(100));