feat: Instanceのエンティティを追加

src/main/kotlin/dev/usbharu/hideout/core/domain/model/instance/Instance.kt

@@ -0,0 +1,15 @@
+package dev.usbharu.hideout.core.domain.model.instance
+
+data class Instance(
+    val id: Long,
+    val name: String,
+    val description: String,
+    val url: String,
+    val iconUrl: String,
+    val sharedInbox: String,
+    val software: String,
+    val version: String,
+    val isBlocked: Boolean,
+    val isMuting: Boolean,
+    val moderationNote: String
+)

src/main/kotlin/dev/usbharu/hideout/core/domain/model/instance/InstanceRepository.kt

@@ -0,0 +1,7 @@
+package dev.usbharu.hideout.core.domain.model.instance
+
+interface InstanceRepository {
+    suspend fun save(instance: Instance): Instance
+    suspend fun findById(id: Long): Instance
+    suspend fun delete(instance: Instance)
+}