feat: 定义仓库协议与用例（含会话）

IosClientKit/Sources/CoreDomain/PlanUseCase.swift

@@ -0,0 +1,22 @@
+import CoreModel
+
+/// 获取/提交计划数据的用例。
+public struct PlanUseCase: Sendable {
+    private let repository: PlanRepository
+
+    public init(repository: PlanRepository) {
+        self.repository = repository
+    }
+
+    public func observePlan(type: PlanType) -> AsyncThrowingStream<PlanRecord, Error> {
+        repository.observePlan(type: type)
+    }
+
+    public func observePlanSubmit(type: PlanType, periodKey: String) -> AsyncThrowingStream<PlanSubmitData, Error> {
+        repository.observePlanSubmit(type: type, periodKey: periodKey)
+    }
+
+    public func savePlan(type: PlanType, periodKey: String, content: String, attachments: [String]) async throws {
+        try await repository.savePlan(type: type, periodKey: periodKey, content: content, attachments: attachments)
+    }
+}