feat(schedules): make schedules pausable

Adds pause/resume support for scheduled prompts.

Backend:
- New paused_at_unix column on scheduled_prompts table (added via
  ALTER TABLE migration so existing databases are upgraded on first
  start). The due-rows index is dropped and recreated to also exclude
  paused rows so the worker never fires them while paused.
- Worker's due() query gains AND paused_at_unix IS NULL filter.
- New pause(id) and resume(id) methods on ScheduledPrompts; both are
  idempotent and refuse cancelled rows.
- New POST /api/schedules/{id}/pause and /api/schedules/{id}/resume
  dashboard endpoints (operator-direct, no approval gate). Both emit
  a schedules snapshot on success so the tab updates live.
- WireSchedule gains paused_at_unix: Option<i64> so the frontend can
  render the state without an extra fetch.

Frontend:
- Paused rows render with a distinct row class + muted opacity.
- The next-fire cell shows a yellow pause glyph + tooltip with the
  paused-since timestamp and the would-have-fired time.
- Actions column: pause/resume toggle button (⏸/▶) beside fire/edit/cancel.
  Fire-now is disabled while paused (resume first).
- Sort order: active → paused → cancelled (paused slot keeps schedules
  visible without mixing them into the active top section).
- pauseSchedule() / resumeSchedule() async functions POST to the new
  endpoints and refresh the table on success.

hive-c0re/src/dashboard/schedules.rs

@@ -228,6 +228,52 @@ pub(super) async fn patch_schedule(
     }
 }
 
+/// `POST /api/schedules/{id}/pause` — pause a schedule so the worker
+/// skips it until explicitly resumed. Idempotent; no-op on an already-
+/// paused row. Returns 404 when the schedule is cancelled or not found.
+pub(super) async fn post_schedule_pause(
+    State(state): State<AppState>,
+    AxumPath(id): AxumPath<i64>,
+) -> Response {
+    match state.coord.scheduled_prompts.pause(id) {
+        Ok(()) => {
+            state.coord.emit_schedules_snapshot();
+            (StatusCode::OK, "ok").into_response()
+        }
+        Err(e) => {
+            let msg = format!("{e:#}");
+            if msg.contains("not found") || msg.contains("cancelled") {
+                (StatusCode::NOT_FOUND, msg).into_response()
+            } else {
+                error_response(&format!("pause schedule {id}: {msg}"))
+            }
+        }
+    }
+}
+
+/// `POST /api/schedules/{id}/resume` — resume a paused schedule.
+/// Idempotent; no-op on an already-active row. Returns 404 when the
+/// schedule is cancelled or not found.
+pub(super) async fn post_schedule_resume(
+    State(state): State<AppState>,
+    AxumPath(id): AxumPath<i64>,
+) -> Response {
+    match state.coord.scheduled_prompts.resume(id) {
+        Ok(()) => {
+            state.coord.emit_schedules_snapshot();
+            (StatusCode::OK, "ok").into_response()
+        }
+        Err(e) => {
+            let msg = format!("{e:#}");
+            if msg.contains("not found") || msg.contains("cancelled") {
+                (StatusCode::NOT_FOUND, msg).into_response()
+            } else {
+                error_response(&format!("resume schedule {id}: {msg}"))
+            }
+        }
+    }
+}
+
 /// `POST /api/schedules/{id}/cancel` — operator-side cancel
 /// (whole schedule when no `targets` field, partial when one is
 /// provided). Operator bypasses the topology check; the manager