fix: adapt for mobile

frontend/src/lib/components/ChatHeader.svelte

@@ -1,4 +1,5 @@
 <script lang="ts">
+  import { goto } from "$app/navigation";
   import {
     enqueueBackfill,
     getCurrentPresence,
@@ -123,6 +124,17 @@
 </script>
 
 <header class="chat-header">
+  <div class="back">
+    <Button
+      variant="translucent"
+      round
+      smaller
+      onclick={() => goto("/app")}
+      aria-label="Назад"
+    >
+      <Icon name="arrow-left" />
+    </Button>
+  </div>
   <ContextMenu>
     {#snippet children({ props })}
       <button
@@ -207,6 +219,15 @@
     background-color: var(--color-background);
   }
 
+  .back {
+    display: none;
+    margin-left: -0.25rem;
+
+    @media (max-width: 600px) {
+      display: block;
+    }
+  }
+
   .peek {
     display: flex;
     flex: 1;