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/README.md

@@ -9,8 +9,8 @@ would hit. HTTP is the sole transport; there is no stdio mode here.
 ## When to use it
 
 This is where the core hyperhive tool surface lives: `send`, `recv`,
-`remind`, `get_loose_ends`, `set_status`,
-`get_agent_meta`, scheduling, and the approval-request tools. Reach
+`remind`, `get_loose_ends`, `set_status`
+and `get_agent_meta`. Reach
 for this crate when you're adding or changing a built-in tool rather
 than an `extraMcpServers` add-on — those are separate stdio bridges
 (see `hive-bash-mcp`, `hive-matrix-mcp`) that dial the harness socket