feat: 定义仓库协议与用例（含会话）

IosClientKit/Sources/CoreDomain/PlanRepository.swift

@@ -0,0 +1,8 @@
+import CoreModel
+
+/// 计划数据仓库协议（定义在 domain 层，实现放 CoreRepository）。
+public protocol PlanRepository: Sendable {
+    func observePlan(type: PlanType) -> AsyncThrowingStream<PlanRecord, Error>
+    func observePlanSubmit(type: PlanType, periodKey: String) -> AsyncThrowingStream<PlanSubmitData, Error>
+    func savePlan(type: PlanType, periodKey: String, content: String, attachments: [String]) async throws
+}