feat: live SSE updates for the SCH3DUL3S tab

Add `SchedulesChanged` to the dashboard event channel so the
operator's schedule list updates in real time without requiring a
tab-activation or form-submit refresh.

Backend:
- `dashboard_events.rs`: new `SchedulesChanged { seq, schedules }`
  variant carrying a full `Vec<WireSchedule>` snapshot (same
  snapshot-over-diff rationale as `RebuildQueueChanged`).
- `coordinator.rs`: `emit_schedules_snapshot()` helper — queries the
  scheduled_prompts list, converts to wire shape, broadcasts the event.
- `dashboard.rs`: call `emit_schedules_snapshot()` at the end of each
  operator API handler that mutates a schedule:
  `post_schedule_new`, `post_schedule_fire_now`,
  `patch_schedule`, `post_schedule_cancel`.
- `scheduled_prompts_worker.rs`: call `emit_schedules_snapshot()`
  after each tick that fires schedules, so `last_fired_at_unix`,
  `next_fire_at_unix`, and reaped one-shots surface live.

Frontend:
- `tabs.js`: add `applySchedulesChanged(ev)` — replaces
  `schedulesState` from the snapshot and calls `renderSchedulesList()`.
  Registered in `MUTATION_HANDLERS` as `schedules_changed`.
  Tab-activation re-fetch kept as safety net for approval-path
  inserts and disconnect windows; comment updated to reflect this.

Docs:
- `docs/web-ui/dashboard.md`: document `schedules_changed` event.
- `CLAUDE.md`: add `SchedulesChanged` to the file-map entry.

hive-c0re/src/coordinator.rs

@@ -368,6 +368,27 @@ impl Coordinator {
         });
     }
 
+    /// Emit a `SchedulesChanged` snapshot event. Called from every
+    /// schedule mutation site (operator API handlers + the worker
+    /// after each tick that fires or rearms a row) so the dashboard's
+    /// scheduled-prompts tab updates live without polling.
+    pub fn emit_schedules_snapshot(self: &Arc<Self>) {
+        let schedules = match self.scheduled_prompts.list() {
+            Ok(rows) => rows
+                .into_iter()
+                .map(crate::manager_server::schedule_to_wire_public)
+                .collect(),
+            Err(e) => {
+                tracing::warn!(error = ?e, "emit_schedules_snapshot: list failed");
+                return;
+            }
+        };
+        self.emit_dashboard_event(DashboardEvent::SchedulesChanged {
+            seq: self.next_seq(),
+            schedules,
+        });
+    }
+
     /// Update the `step` label on a running queue entry and (if it
     /// actually changed) re-emit the queue snapshot so the dashboard
     /// renders the new phase. Returns `true` when the label was new