feat(store): add test for clearing dispatch error on successful merge

- Introduced a new test case in speaker_meta_test.go to verify that the LastDispatchError is cleared when a successful dispatch status is merged.
- Updated MergeSpeakerMetaJSON function in speaker_meta.go to clear LastDispatchError if LastDispatchStatus is "ok".
- Enhanced speakerDispatchError function in network-metrics.ts to handle stale dispatch errors after successful agent sync.

internal/store/speaker_meta.go

@@ -72,7 +72,9 @@ func MergeSpeakerMetaJSON(existing string, patch SpeakerMeta) string {
 	if patch.LastDispatchAt != "" {
 		cur.LastDispatchAt = patch.LastDispatchAt
 	}
-	if patch.LastDispatchError != "" {
+	if patch.LastDispatchStatus == "ok" {
+		cur.LastDispatchError = ""
+	} else if patch.LastDispatchError != "" {
 		cur.LastDispatchError = patch.LastDispatchError
 	}
 	if patch.LastDispatchStatus != "" {