New Feature: Add server-side channel unreads.

src/database/entities/sync.rs

@@ -1,3 +1,19 @@
 use std::collections::HashMap;
+use serde::{Serialize, Deserialize};
 
 pub type UserSettings = HashMap<String, (i64, String)>;
+
+#[derive(Serialize, Deserialize, Debug, Clone)]
+pub struct ChannelCompositeKey {
+    pub channel: String,
+    pub user: String,
+}
+
+#[derive(Serialize, Deserialize, Debug, Clone)]
+pub struct ChannelUnread {
+    #[serde(rename = "_id")]
+    pub id: ChannelCompositeKey,
+
+    pub last_id: String,
+    pub mentions: Option<Vec<String>>,
+}