feat: 新增 Mock 数据层与依赖容器（含单元测试）

app/src/main/java/com/placeholder/ringhealth/AppContainer.kt

@@ -0,0 +1,20 @@
+package com.placeholder.ringhealth
+
+import com.placeholder.ringhealth.data.mock.MockHealthDataRepository
+import com.placeholder.ringhealth.data.mock.MockRingDeviceRepository
+import com.placeholder.ringhealth.domain.repository.HealthDataRepository
+import com.placeholder.ringhealth.domain.repository.RingDeviceRepository
+
+/**
+ * 手动依赖注入容器。M2 接入 SDK 时只需在这里把 Mock 实现换成真实实现。
+ */
+interface AppContainer {
+    val healthDataRepository: HealthDataRepository
+    val ringDeviceRepository: RingDeviceRepository
+}
+
+/** 默认容器：阶段一全部使用 Mock 数据。 */
+class DefaultAppContainer : AppContainer {
+    override val healthDataRepository: HealthDataRepository = MockHealthDataRepository()
+    override val ringDeviceRepository: RingDeviceRepository = MockRingDeviceRepository()
+}