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/dashboard_events.rs

@@ -192,6 +192,16 @@ pub enum DashboardEvent {
     /// dashboard's grouping (`parent_id`) is most naturally re-derived
     /// from the full list.
     RebuildQueueChanged { seq: u64, queue: Vec<QueueEntry> },
+    /// Full snapshot of all scheduled prompts. Emitted after every
+    /// operator mutation (new / edit / cancel / fire-now) and after the
+    /// worker fires or rearms a row. Same snapshot-shape rationale as
+    /// `RebuildQueueChanged` — the list is small and the client's
+    /// per-target `last_result` / `last_fired_at_unix` fields are most
+    /// naturally re-derived from the full list.
+    SchedulesChanged {
+        seq: u64,
+        schedules: Vec<hive_sh4re::WireSchedule>,
+    },
 }
 
 impl DashboardEvent {
@@ -222,6 +232,7 @@ impl DashboardEvent {
             DashboardEvent::MetaInputsChanged { .. } => "meta_inputs_changed",
             DashboardEvent::MetaUpdateRunning { .. } => "meta_update_running",
             DashboardEvent::RebuildQueueChanged { .. } => "rebuild_queue_changed",
+            DashboardEvent::SchedulesChanged { .. } => "schedules_changed",
         }
     }
 }
@@ -340,6 +351,10 @@ mod tests {
                 seq: 1,
                 queue: Vec::new(),
             },
+            DashboardEvent::SchedulesChanged {
+                seq: 1,
+                schedules: Vec::new(),
+            },
         ];
         for ev in samples {
             let v: serde_json::Value = serde_json::to_value(&ev).expect("serialise");