dashboard: queued reminders surface

new 'qu3u3d r3m1nd3rs' section between approvals and operator
inbox. lists every pending reminder with agent, due-relative
timestamp, body, payload path (path-linkified), and a cancel
button. drives off a new /api/reminders endpoint and a
POST /cancel-reminder/{id} that hard-deletes the row.

failure surface (last_error / attempt_count + retry) deferred —
needs a sqlite migration; tracked in TODO.md.

hive-c0re/src/dashboard.rs

@@ -55,6 +55,8 @@ pub async fn serve(port: u16, coord: Arc<Coordinator>) -> Result<()> {
         .route("/purge-tombstone/{name}", post(post_purge_tombstone))
         .route("/api/journal/{name}", get(get_journal))
         .route("/api/state-file", get(get_state_file))
+        .route("/api/reminders", get(api_reminders))
+        .route("/cancel-reminder/{id}", post(post_cancel_reminder))
         .route("/api/agent-config/{name}", get(get_agent_config))
         .route("/request-spawn", post(post_request_spawn))
         .route("/op-send", post(post_op_send))
@@ -983,6 +985,27 @@ async fn get_state_file(
     ([("content-type", "text/plain; charset=utf-8")], body).into_response()
 }
 
+async fn api_reminders(State(state): State<AppState>) -> Response {
+    match state.coord.broker.list_pending_reminders() {
+        Ok(rows) => axum::Json(rows).into_response(),
+        Err(e) => error_response(&format!("reminders: {e:#}")),
+    }
+}
+
+async fn post_cancel_reminder(
+    State(state): State<AppState>,
+    AxumPath(id): AxumPath<i64>,
+) -> Response {
+    match state.coord.broker.cancel_reminder(id) {
+        Ok(0) => error_response(&format!("reminder {id} not pending (already delivered?)")),
+        Ok(_) => {
+            tracing::info!(%id, "operator cancelled reminder");
+            (StatusCode::OK, "ok").into_response()
+        }
+        Err(e) => error_response(&format!("cancel reminder {id} failed: {e:#}")),
+    }
+}
+
 async fn post_purge_tombstone(
     State(state): State<AppState>,
     AxumPath(name): AxumPath<String>,