feat(ssf): 实现安全事件一键连接与凭据托管

新增数据库驱动的 SecurityEventConnectionManager，复用 RFC 7662 机器 Client，自动完成 Discovery、Push Bearer 生成、Stream 创建、Verification、首次启用、零停机轮换和安全退役。

增加文件与 Kubernetes SecretStore、最小权限 RBAC、动态 Receiver/撤销水位/内省降级，以及系统设置管理页面。已通过全量 Go 测试、go vet、关键包竞态测试、27 个 Web 测试、类型检查、生产构建、Compose 和 Kubernetes dry-run。

deploy/kubernetes/security-events-secret-rbac.yaml

@@ -0,0 +1,34 @@
+# Reference overlay for installations that run the Gateway in Kubernetes.
+# Keep the Secret empty: the Gateway writes only generated Push Bearers.
+apiVersion: v1
+kind: Secret
+metadata:
+  name: easyai-gateway-security-events
+  namespace: easyai
+type: Opaque
+data: {}
+---
+apiVersion: rbac.authorization.k8s.io/v1
+kind: Role
+metadata:
+  name: easyai-gateway-security-events
+  namespace: easyai
+rules:
+  - apiGroups: [""]
+    resources: ["secrets"]
+    resourceNames: ["easyai-gateway-security-events"]
+    verbs: ["get", "update", "patch"]
+---
+apiVersion: rbac.authorization.k8s.io/v1
+kind: RoleBinding
+metadata:
+  name: easyai-gateway-security-events
+  namespace: easyai
+subjects:
+  - kind: ServiceAccount
+    name: easyai-ai-gateway
+    namespace: easyai
+roleRef:
+  apiGroup: rbac.authorization.k8s.io
+  kind: Role
+  name: easyai-gateway-security-events