Refactor: Make Avatar in UserItem customisable

src/comp/useritem.svelte

@@ -1,22 +1,21 @@
 <script>
+  import Avatar from "./avatar.svelte";
   import Mention from "./mention.svelte";
 
   /**
    * @type {import("$types/base").User | undefined | null}
    */
   export let user;
+
+  /**
+   * @type {number}
+   */
+  export let iconSize = 16;
 </script>
 
 <style>
-  .icon {
-    width: 16px;
-    height: 16px;
-    border-radius: 100%;
-  }
 </style>
 
 <Mention user={user}>
-  <svg class="icon" viewBox="0 0 100 100">
-    <use href="/avatar.svg#avatar"></use>
-  </svg>
+  <Avatar size={iconSize}></Avatar>
 </Mention>