fix remaining event bus contract violations

- event_scheduler: hardcode Scheduler category for ScheduledEventFired
  instead of using sched.category (latent mismatch)
- event_store: fix test helper category to match OrchestratorStarted payload
- event_reactor: fix test ChainHandler category to match OrchestratorStarted payload

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: odgrim

src/services/event_reactor.rs

@@ -1171,7 +1171,7 @@ mod tests {
                     sequence: SequenceNumber(0),
                     timestamp: Utc::now(),
                     severity: EventSeverity::Info,
-                    category: EventCategory::Task,
+                    category: EventCategory::Orchestrator,
                     goal_id: None,
                     task_id: None,
                     correlation_id: event.correlation_id,

src/services/event_scheduler.rs

@@ -376,7 +376,7 @@ impl EventScheduler {
                                 sequence: SequenceNumber(0),
                                 timestamp: now,
                                 severity: sched.severity,
-                                category: sched.category,
+                                category: EventCategory::Scheduler,
                                 goal_id: sched.goal_id,
                                 task_id: sched.task_id,
                                 correlation_id: None,

src/services/event_store.rs

@@ -726,7 +726,7 @@ mod tests {
             sequence: SequenceNumber(seq),
             timestamp: Utc::now(),
             severity: EventSeverity::Info,
-            category: EventCategory::Task,
+            category: EventCategory::Orchestrator,
             goal_id: None,
             task_id: None,
             correlation_id: None,