fix(bugseti): acquire mutex in NewQueueService before load()

q.load() accesses shared state (issues, seen, current) without holding
the mutex, creating a race condition. Wrap the call with q.mu.Lock().

Fixes #52

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

internal/bugseti/queue.go

@@ -103,7 +103,9 @@ func NewQueueService(config *ConfigService) *QueueService {
 		seen:   make(map[string]bool),
 	}
 	heap.Init(&q.issues)
+	q.mu.Lock()
 	q.load() // Load persisted queue
+	q.mu.Unlock()
 	return q
 }