feat(spec): pin org-feishu app binding to 1:1

- FeishuConnection.lean: FeishuAppBinding (appId + appSecretEnvelope)
- Organization.feishu: Option FeishuAppBinding (Option 自带 1:1)
- 删除 FeishuConnectionId (不再需要游离类型)
- FeishuProfile 删除 connection 字段 (由 org 隐含)

spec/Spec/System.lean

@@ -2,6 +2,7 @@ import Spec.System.Hierarchy
 import Spec.System.ProjectGroup
 import Spec.System.Organization
 import Spec.System.User
+import Spec.System.FeishuConnection
 import Spec.System.ProjectWorkspace
 import Spec.System.Capacity
 import Spec.System.PlatformAdministration