fix(FN-1818): fix milestone/slice status tracking on feature changes

- Add SSE listener for milestone:updated events in MissionManager to refresh UI on status changes
- Trigger slice and milestone status recompute when task feature status changes
- Add diagnostic log when task feature resolution fails for easier debugging
- Add regression tests for milestone status recompute logic

packages/engine/src/scheduler.ts

@@ -728,6 +728,7 @@ export class Scheduler {
 
       const feature = this.resolveMissionFeatureForTask(missionStore, task);
       if (!feature) {
+        schedulerLog.log(`No linked feature found for task ${taskId} (sliceId=${task.sliceId ?? "none"}) — skipping mission status update`);
         return;
       }