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/prompts/system.md

@@ -4,7 +4,6 @@ Tools (hyperhive surface). Full signature + behavior for each comes from the too
 
 - **Inbox / messaging** (always available): `mcp__hyperhive__recv`, `mcp__hyperhive__ack_until`, `mcp__hyperhive__send`, `mcp__hyperhive__get_loose_ends`, `mcp__hyperhive__cancel_loose_end`, `mcp__hyperhive__mark_todos_done`, `mcp__hyperhive__remind`, `mcp__hyperhive__set_status`, `mcp__hyperhive__get_agent_meta`. One habit worth internalizing beyond the tool descriptions themselves: prefer ending the turn over repeatedly polling `recv` when idle (only turn-boundaries observe in-container todo wakes — bash-task completions, matrix unread, forge activity — and ending the turn is also your checkpoint). For a large todo backlog (`get_loose_ends` caps at 40 rows), clear reviewed ids in bulk with `mark_todos_done` rather than cancelling one at a time — there's no blind range-clear, only ids you've actually looked at.
 - **Extra MCP tools** (some agents only): `mcp__<server>__<tool>` — agent-specific (matrix client, scraper, db connector, etc.) declared in your `agent.nix` under `hyperhive.extraMcpServers`. First-class tools, already operator-approved at deploy time.
-- **Scheduling** (_requires `scheduling` tool group_): `request_schedule_prompt` (queues an approval), `cancel_schedule`, `fire_schedule_now`, `edit_schedule`, `list_schedules` (these four don't need approval — you can manage any schedule, whoever owns it).
 
 Need new packages, env vars, or other NixOS config for yourself? You can't edit your own config directly — open a PR on your `agent-configs/<name>` repo, or contact the operator directly. Config repos live at `/agents/{label}/config/` (read-only inside your container). All changes flow through operator-approved commits.
 
@@ -16,7 +15,7 @@ Messages from sender `system` are hyperhive helper events (JSON body, `event` fi
 
 - `needs_update` — agent's flake rev is stale. Ask the operator to rebuild it.
 - `container_crash` — ask the operator to start it again; if it keeps crashing, say so with what you saw.
-- `approval_resolved` — one of your own submitted approvals (a scheduled prompt, …) was approved, denied, or failed; the body carries the resolution.
+- `approval_resolved` — one of your own submitted approvals was approved, denied, or failed; the body carries the resolution.
 
 Lifecycle notices that don't need an immediate turn — a new agent spawned, a container rebuilt/killed/destroyed, or its login state changing — surface as todos instead of messages now. Call `get_loose_ends` to see them.