refactor(spec): generalize Feishu to Connections

- Connections/Prelude.lean: ConnectionProvider 枚举 (当前仅飞书)
- Connections/Feishu.lean: FeishuAppBinding + FeishuProfile
- Connections.lean: ConnectionBinding/ConnectionProfile inductive
- Organization.feishu → connections: List ConnectionBinding
- User.feishu → connections: List ConnectionProfile
- 删除 FeishuConnection.lean

spec/Spec/System/Connections.lean

@@ -0,0 +1,24 @@
+import Spec.System.Connections.Prelude
+import Spec.System.Connections.Feishu
+
+/-!
+# Connections —— 连接绑定与用户信息
+
+组织/用户的外部连接。提供商枚举见 `Connections.Prelude`;
+飞书具体类型见 `Connections.Feishu`。
+-/
+
+namespace Spec.System
+
+
+/-- 组织连接绑定(`PINNED`)。 -/
+inductive ConnectionBinding (I : Identifiers) where
+  /-- 飞书(`PINNED`)。 -/
+  | feishu : FeishuAppBinding I → ConnectionBinding I
+
+/-- 用户连接信息(`PINNED`)。 -/
+inductive ConnectionProfile (I : Identifiers) where
+  /-- 飞书(`PINNED`)。 -/
+  | feishu : FeishuProfile I → ConnectionProfile I
+
+end Spec.System