feat(operator): add queue-operator CRD reconciler with shard split/drain

Reconciles Queue CRs into Kafka topics + Redis shard-map/queue-meta state:
creates shard-0 on first reconcile, splits a shard's hash range into two
children once its split threshold is crossed, drains and closes a parent
shard once its consumer group has fully caught up and its retention
window has elapsed, and tears down every shard's topic + Redis state on
deletion. Includes the manager entrypoint (cmd/queue-operator) and RBAC.

internal/operator/admin.go

@@ -0,0 +1,16 @@
+package operator
+
+import (
+	"context"
+
+	"github.com/rockliang/kafka-management-service/internal/kafka"
+)
+
+// TopicAdmin is the subset of internal/kafka.Admin the reconciler needs,
+// abstracted so tests can substitute a fake instead of a real Kafka cluster.
+type TopicAdmin interface {
+	CreateTopic(ctx context.Context, topic string, cfg kafka.TopicConfig) error
+	DeleteTopic(ctx context.Context, topic string) error
+	LogEndOffsetSum(ctx context.Context, topic string) (int64, error)
+	ConsumerLag(ctx context.Context, group, topic string) (int64, error)
+}