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.rs

@@ -1964,7 +1964,10 @@ async fn post_schedule_new(
         source: crate::scheduled_prompts::ScheduleSource::Operator,
     };
     match state.coord.scheduled_prompts.submit(&new) {
-        Ok(id) => axum::Json(serde_json::json!({"id": id})).into_response(),
+        Ok(id) => {
+            state.coord.emit_schedules_snapshot();
+            axum::Json(serde_json::json!({"id": id})).into_response()
+        }
         Err(e) => error_response(&format!("schedule submit: {e:#}")),
     }
 }
@@ -1982,7 +1985,10 @@ async fn post_schedule_fire_now(
     AxumPath(id): AxumPath<i64>,
 ) -> Response {
     match crate::scheduled_prompts_worker::fire_now(&state.coord, id).await {
-        Ok(report) => axum::Json(report).into_response(),
+        Ok(report) => {
+            state.coord.emit_schedules_snapshot();
+            axum::Json(report).into_response()
+        }
         Err(e) => error_response(&format!("fire schedule {id} now: {e:#}")),
     }
 }
@@ -2093,7 +2099,9 @@ async fn patch_schedule(
     }
     match state.coord.scheduled_prompts.get(id) {
         Ok(Some(s)) => {
-            axum::Json(crate::manager_server::schedule_to_wire_public(s)).into_response()
+            let wire = crate::manager_server::schedule_to_wire_public(s);
+            state.coord.emit_schedules_snapshot();
+            axum::Json(wire).into_response()
         }
         Ok(None) => error_response(&format!("edit schedule {id}: row vanished post-update")),
         Err(e) => error_response(&format!("re-read schedule {id}: {e:#}")),
@@ -2117,7 +2125,10 @@ async fn post_schedule_cancel(
         None => state.coord.scheduled_prompts.cancel_all(id),
     };
     match result {
-        Ok(()) => (StatusCode::OK, "ok").into_response(),
+        Ok(()) => {
+            state.coord.emit_schedules_snapshot();
+            (StatusCode::OK, "ok").into_response()
+        }
         Err(e) => error_response(&format!("cancel schedule {id}: {e:#}")),
     }
 }