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-sh4re/src/manager.rs

@@ -1,8 +1,7 @@
 //! Manager socket — `/run/hyperhive/manager/mcp.sock` on the host,
 //! bind-mounted into the manager container at `/run/hive/mcp.sock`.
-//! Reserved recipient names/senders, the out-of-band `HelperEvent`
-//! payload hive-c0re pushes into the manager's inbox, and the
-//! schedule-prompt submission payload.
+//! Reserved recipient names/senders and the out-of-band `HelperEvent`
+//! payload hive-c0re pushes into the manager's inbox.
 
 use hive_types::Ident;
 use serde::{Deserialize, Serialize};
@@ -66,30 +65,6 @@ pub enum HelperEvent {
     },
 }
 
-/// Submission payload for `RequestSchedulePrompt`. Lives outside the
-/// enum so it can also serialize into the approval row's `commit_ref`
-/// (the dispatcher re-parses it on approve and inserts the schedule).
-#[derive(Debug, Clone, Serialize, Deserialize, PartialEq, Eq)]
-pub struct SchedulePromptPayload {
-    /// Names of recipient agents. Operator + `root` allowed.
-    pub targets: Vec<String>,
-    /// Message body delivered to each target's inbox at fire time.
-    /// Same size budget as `Send.body` — soft cap at the broker level.
-    pub body: String,
-    /// Absolute unix timestamp (seconds) for the FIRST fire. For
-    /// recurring schedules the worker then re-arms in
-    /// `interval_seconds` steps.
-    pub first_fire_at_unix: i64,
-    /// `None` = one-shot. `Some(n > 0)` = recurring every `n` seconds.
-    #[serde(default, skip_serializing_if = "Option::is_none")]
-    pub interval_seconds: Option<u64>,
-    /// Optional description shown on the dashboard approval card AND
-    /// stored on the resulting schedule row for the operator's
-    /// "what is this?" reference later.
-    #[serde(default, skip_serializing_if = "Option::is_none")]
-    pub description: Option<String>,
-}
-
 #[cfg(test)]
 mod reserved_name_tests {
     use super::{MANAGER_AGENT, OPERATOR_RECIPIENT, SYSTEM_SENDER};