start fill server part

Core/src/main/kotlin/com/insanusmokrassar/postssystem/core/api/ReadPostsAPI.kt

@@ -13,5 +13,5 @@ interface ReadPostsAPI {
     suspend fun getPostsByContent(id: ContentId): List<Post>
     suspend fun getPostsByDates(from: DateTime? = null, to: DateTime? = null): List<Post>
 
-    suspend fun getPostsByPagination(pagination: Pagination): PaginationResult<Post>
+    suspend fun getPostsByPagination(pagination: Pagination): PaginationResult<out Post>
 }

Core/src/main/kotlin/com/insanusmokrassar/postssystem/core/post/Post.kt

@@ -1,6 +1,7 @@
 package com.insanusmokrassar.postssystem.core.post
 
 import com.insanusmokrassar.postssystem.core.content.Content
+import kotlinx.serialization.Serializable
 
 typealias PostId = String
 typealias PostContents = List<Content>
@@ -10,4 +11,11 @@ interface Post {
     val content: PostContents
 
     val meta: PostMetaInfo
-}
+}
+
+@Serializable
+data class SimplePost(
+    override val id: PostId,
+    override val content: PostContents,
+    override val meta: PostMetaInfo
+) : Post